a tool to improve and preserve flexible pavement at
TRANSCRIPT
University of Texas at El PasoDigitalCommons@UTEP
Open Access Theses & Dissertations
2010-01-01
A Tool to Improve and Preserve Flexible Pavementat IntersectionsCarlos Jesus SolisUniversity of Texas at El Paso, [email protected]
Follow this and additional works at: https://digitalcommons.utep.edu/open_etdPart of the Civil Engineering Commons
This is brought to you for free and open access by DigitalCommons@UTEP. It has been accepted for inclusion in Open Access Theses & Dissertationsby an authorized administrator of DigitalCommons@UTEP. For more information, please contact [email protected].
Recommended CitationSolis, Carlos Jesus, "A Tool to Improve and Preserve Flexible Pavement at Intersections" (2010). Open Access Theses & Dissertations.2786.https://digitalcommons.utep.edu/open_etd/2786
A TOOL TO IMPROVE AND PRESERVE
FLEXIBLE PAVEMENT AT
INTERSECTIONS
CARLOS JESUS SOLIS
Department of Civil Engineering
APPROVED:
Soheil Nazarian, Ph.D.
Vivek Tandon, Ph.D.
Peter Golding, Ph.D.
Patricia D. Witherspoon, Ph.D. Dean of the Graduate School
A TOOL TO IMPROVE AND PRESERVE
FLEXIBLE PAVEMENT AT
INTERSECTIONS
by
CARLOS JESUS SOLIS, B.S.C.E.
THESIS
Presented to the Faculty of the Graduate School of
The University of Texas at El Paso
in Partial Fulfillment
of the Requirements
for the Degree of
MASTER OF SCIENCE
Department of Civil Engineering
THE UNIVERSITY OF TEXAS AT EL PASO
May 2010
iii
TABLE OF CONTENTS
Table of Contents........................................................................................................................... iii
List of Tables ................................................................................................................................ vii
List of Figures .............................................................................................................................. viii
Aknowledgments .............................................................................................................................1
Chapter 1: Introduction ...................................................................................................................2
1.1 Background....................................................................................................................2
1.1.1 Low-volume Roads...............................................................................................3
1.1.2 Traffic ...................................................................................................................3
1.2 Objectives ......................................................................................................................5
1.3 Scope of Study ...............................................................................................................5
1.4 Organization of Thesis...................................................................................................6
Chapter 2: Review of Literature .....................................................................................................7
2.1 Overview of Road Intersection Conditions....................................................................7
2.2 Common Types of Distress on Asphalt Pavements.......................................................7
2.2.1 Rutting...................................................................................................................7
2.2.2 Shoving ...............................................................................................................11
2.2.3 Fatigue Cracking.................................................................................................12
2.2.4 Other Distresses ..................................................................................................12
2.3 Remediation Strategies of Asphalt Pavement at Intersections ....................................13
2.3.1 Current TxDOT Specifications for Flexible Pavement Rehabilitation...............14
2.3.2 Asphalt Institute ..................................................................................................15
2.3.3 Canada.................................................................................................................21
2.3.4 Colorado Department of Transportation (CDOT) ..............................................21
2.3.5 Australia..............................................................................................................23
2.3.6 New Zealand .......................................................................................................25
2.3.7 Illinois DOT........................................................................................................25
2.3.8 Hot Mix Asphalt Mixtures for Nevada’s Intersections.......................................27
2.3.9 National Center for Asphalt Technology (NCAT) .............................................28
2.4 Remediation Strategies Considering Subsurface Layers of Pavements ......................29
iv
2.4.1 Base Layer ..........................................................................................................29
2.4.2 Subgrade Layer ...................................................................................................34
2.6 Current Flexible Pavement Design Software and Limitations ....................................41
2.6.1 TxDOT Flexible Pavement Design System (FPS-19) ........................................41
2.6.2 AASHTO’s DARWin .........................................................................................42
2.7 Cost and Benefit Analysis............................................................................................43
2.7.1 Cost Analysis ......................................................................................................43
2.7.2 Life-Cycle Cost Analysis....................................................................................44
2.8 Summary......................................................................................................................45
Chapter 3: Research Approach .....................................................................................................49
3.1 Texas Districts Surveys................................................................................................49
Question 1: Do your pavements experience distress at the intersections of low volume roads? .....................................................................................................49
Question 2: If yes, what percentage of the intersections experiences any type of distress?...............................................................................................................49
Question 3: Approximately what percentages of distressed intersections experience the following distress severity? (total for the three categories should be 100%) .................................................................................................51
Low Severity (___%) Medium Severity (____%) High Severity (___%)...............51
Question 4: What distress types are common at your intersections on low volume roads? ..................................................................................................................52
Question 5-9 referred to the all five distresses listed in Question 4. ...........................52
Question 10: Please fill the table below regarding solutions you typically use to remedy each distress and provide typical performance life of each remedy. .....53
3.2 Methodology................................................................................................................55
3.2.1 Input Data............................................................................................................56
3.2.2 Evaluation ...........................................................................................................57
3.2.3 Remediation Strategies .......................................................................................59
3.2.4 Life-Cycle Cost Analysis....................................................................................63
3.2.5 Output .................................................................................................................64
Chapter 4: Case Study: Intersection of SH 155 and SH 49 Forensic Evaluation ........................65
4.1 Background..................................................................................................................65
4.2 Condition Survey .........................................................................................................66
4.2 Data Collection ............................................................................................................69
v
4.3 Data Analysis ...............................................................................................................70
4.3.1 Core Analysis ......................................................................................................70
4.3.2 FWD Analysis .....................................................................................................74
4.3.3 GPR Analysis......................................................................................................76
4.4 Conclusions..................................................................................................................78
Chapter 5: Excel Spreadsheet Analysis of SH 155 and SH 49 Intersection .................................80
5.1 Section 1: General Project Information ......................................................................80
5.2 Section 2: Analysis Options........................................................................................81
5.3 Section 3: Traffic Conditions......................................................................................82
5.4 Section 4: Evaluate Existing Pavement Condition .....................................................83
5.5 Section 5: Repair Alternatives ....................................................................................84
5.6 Section 6: Life Cycle Cost Analysis ...........................................................................85
Chapter 6: Summary and Conclusions..........................................................................................89
6.1 Summary......................................................................................................................89
6.2 Recommendations and Future Work ...........................................................................91
References......................................................................................................................................92
Appendix A: TxDOT Research Project 0-5566 Questionnaire ....................................................97
Appendix B: Summary of Questionnaire....................................................................................101
Appendix C: Excel Spreadsheet Interface Manual .....................................................................107
C.1 Section 1: General Project Information .....................................................................108
C.2 Section 2: Analysis Options.......................................................................................109
C.3 Section 3: Traffic Conditions.....................................................................................110
C.4 Section 4: Evaluate Existing Pavement Condition ....................................................111
C.5 Section 5: Repair Alternatives ...................................................................................111
C.6 Section 6: Life Cycle Cost Analysis ..........................................................................113
C.7 Cost and Life Expectancy Sheet ................................................................................117
C.8 Remediation Methods Table Sheet ............................................................................118
C.9 Program Decision Tree ..............................................................................................120
C.10 LCCA Sheet ...............................................................................................................120
C.11 ESAL Tables Sheet ....................................................................................................121
C.12 Common Distresses and Remediation Strategies Sheets ...........................................123
vi
Appendix D: Remediation Strategies..........................................................................................126
Microsurfacing....................................................................................................................127
Fog Seal ..............................................................................................................................128
Crack seal............................................................................................................................128
Sand Seal.............................................................................................................................129
Slurry Seal...........................................................................................................................129
Chip Seals ...........................................................................................................................129
Hot In-place recycling (HIPR)............................................................................................130
Cold In-place Recycling (CIPR).........................................................................................130
HMA & Recycled Asphalt Shingles (RAS) Overlay..........................................................131
PCC Overlay (Thick) ..........................................................................................................131
Ultra-thin Whitetopping......................................................................................................131
Full Depth Reclamation ......................................................................................................132
Appendix E: Core Summaries from Intersection of SH49 and SH155 ......................................133
Appendix F: Check Lists for Future Site Visits..........................................................................140
Current Pavement Design ...................................................................................................143
Traffic Information .............................................................................................................143
Visual Survey......................................................................................................................143
Non Destructive Testing .....................................................................................................144
Destructive Testing .............................................................................................................144
Laboratory Testing..............................................................................................................145
Vita ............................................................................................................................................146
vii
LIST OF TABLES
Table 2.1: Superpave Binder (PGAC) Selection Adjustments (Bumping) for Design ESALs and Loading Rate................................................................................................................................. 18 Table 2.2: Stabilization Methods for Different Soil Types (Terrel et al., 1979) ......................... 32 Table 2.3: Geotextile Specifications for construction Survivability in Low-Cost Low-Volume Roads (from Cicoff and Sprague, 1991) ....................................................................................... 41 Table 3.1: Distribution of Trucks on Different Classes of Highways in the United States after AI (1991)............................................................................................................................................ 61 Table 3.2: Distribution of Truck Factors for Different Classes of Highways and Vehicles in the United States after AI (1991)........................................................................................................ 62 Table 3.3: Lane Distribution Factor after AASHTO (1986)........................................................ 63 Table B.1: Summary of Causes of Rutting for each District ..................................................... 102 Table B.2: Summary of Causes of Shoving for each District.................................................... 102 Table B.3: Summary of Causes of Cracking for each District .................................................. 103 Table B.4: Summary of Causes of Pushing for each District .................................................... 103 Table B.5: Summary of Causes of Other Distresses for each District....................................... 104 Table B.6: Summary of Remediation Strategies for Rutting..................................................... 104 Table B.7: Summary of Remediation Strategies for Shoving.................................................... 105 Table B.8: Summary of Remediation Strategies for Cracking .................................................. 105 Table B.9: Summary of Remediation Strategies for Pushing .................................................... 106 Table B.10: Summary of Remediation Strategies for Other Distresses..................................... 106 Table F.1a: A Checklist of Information that Should be Collected at Intersections (Part1). ...... 141 Table F.1b: A Checklist of Information that Should be Collected at Intersections (Part2)....... 141 Table F.1c: A Checklist of Information that Should be Collected at Intersections (Part3). ...... 142
viii
LIST OF FIGURES
Figure 2.1: Structural Rutting on Asphalt Pavements (Federation of Canadian Municipalities and Canadian National Research Council, 2003). ................................................................................. 8 Figure 2.2: Surface Deformation Due to Base and Subgrade Failure. (Fang, 2001).................... 9 Figure 2.3: Instability or Plastic Flow on Asphalt Pavements (Federation of Canadian Municipalities and Canadian National Research Council 2003). ................................................... 9 Figure 2.4: Wear Rutting on Asphalt Pavements (Federation of Canadian Municipalities and Canadian National Research Council 2003). ................................................................................ 11 Figure 2.5: Shoving on Asphalt Pavements................................................................................. 12 Figure 2.6: Shoving on Asphalt Pavements................................................................................. 13 Figure 2.7: Flowchart of Activities for Mitigating Intersection Rutting. .................................... 22 Figure 2.8: TxDOT Flowchart for Base Treatment (TxDOT, 2005a). ........................................ 31 Figure 2.9: Improving Pavement by Using Geosynthetics (from Hopkins et al., 2005). ............ 40 Figure 2.10: Probable Appropriate Remediation for Different Layers........................................ 46 Figure 2.11: Remediation Strategies for Common Distress Indicators. ...................................... 48 Figure 3.1: Results of Survey Responses to Districts Experiencing Distress at the Intersections of Low Volume Roads. ................................................................................................................. 50 Figure 3.2: Percent of Intersections Experiencing Distress in the Districts. ............................... 50 Figure 3.3: Distribution of Distress Severity at Distressed Intersections. ................................... 51 Figure 3.4: Type of Distress at Intersections. .............................................................................. 52 Figure 3.5: Question 5 from the Survey....................................................................................... 52 Figure 3.6: Causes of Distress for Each Type of Distress. .......................................................... 53 Figure 3.7: Remediation Strategies for Distresses at Intersections.............................................. 54 Figure 3.8: Typical Performance Period for Selected Remediation Strategies. .......................... 55 Figure 3.9: Methodology Diagram. ............................................................................................. 56 Figure 4.1: Aerial View of SH 155 and SH 49 Intersection. ....................................................... 65 Figure 4.2: Cross-sectional Pavement Design for SH 155 and SH 49......................................... 66 Figure 4.3: Geometry Design of SH 155 and SH 49 Intersection ............................................... 67 Figure 4.4: Views of the Conditions of SH 155 and SH 49 Intersection..................................... 67 Figure 4.5: Rut Depth Measurement on SH 155.......................................................................... 68 Figure 4.6: Cracking Resulting in Potholes on SH49. ................................................................. 68 Figure 4.7: Location of the Core Extractions............................................................................... 69 Figure 4.8: FWD Collection on SH155 and SH49 Images.......................................................... 70 Figure 4.9: Coring Process Images. ............................................................................................. 70 Figure 4.11: Core Average Thicknesses as Approaching the Intersection. ................................. 71 Figure 4.12: Core Average Air Voids as Approaching the Intersection...................................... 72 Figure 4.13: Core Average Design Modulus as Approaching the Intersection. .......................... 72 Figure 4.14: Core Asphalt Contents............................................................................................. 73 Figure 4.15: Phenolphthalein Test for Lime on Base Material.................................................... 73 Figure 4.16: FWD Deflection Results on Southbound SH 155. .................................................. 74 Figure 4.17: FWD Deflection Results on Eastbound SH 49. ....................................................... 75 Figure 4.18- Sample of the GPR Data Close to the Intersection of FM155 and FM49................ 76 Figure 4.19: GPR, FWD and Cores on SH155. ........................................................................... 77 Figure 4.19: GPR, FWD and Cores on SH49. ............................................................................. 78 Figure 5.1: Section No. 1 with General Project Information Input. ............................................ 81
ix
Figure 5.2: Section No. 2 with Information about LCCA Analysis Options............................... 81 Figure 5.3: Schematic of the Recommended Area for Repair on SH 155. .................................. 82 Figure 5.4: Traffic Conditions Input Parameters. ........................................................................ 83 Figure 5.5: Section No. 4 for the Evaluation of the Existing Pavement...................................... 83 Figure 5.6: Section 5 Tables for Costs and Life Expectancies. ................................................... 85 Figure 5.7: Section No. 6 with Ranked Cost Results................................................................... 86 Figure 5.8: All Alternative Present Value Comparison Graph. ................................................... 86 Figure 5.9: LCCA Plot for the Most Economical Alternative. .................................................... 87 Figure 5.10: LCCA Plot for Full Depth Reclamation with Stabilization .................................... 88 Figure C.1 – Section No. 1 General Project Information. .......................................................... 109 Figure C.2 – Section No. 2 with Analysis Options Input. .......................................................... 110 Figure C.3 – Section No. 3 with Traffic Conditions Input. ........................................................ 111 Figure C.4 – Section No. 4 for the Evaluation of the Existing Pavement. ................................. 111 Figure C.5 – Section No. 5 with all the Possible Alternatives.................................................... 112 Figure C.6 – Section No. 5 Table for Maintenance Method Selection....................................... 113 Figure C.7 – Section No. 6 with Ranked Cost Results. .............................................................. 115 Figure C.8 – Section No. 6 All Alternative Present Value Comparison Graph.......................... 116 Figure C.9 – Section No. 6 LCCA Plot for the Most Economical Alternative........................... 116 Figure C.10 – Section No. 6 LCCA Plot for a Selected Alternative. ......................................... 117 Figure C.11 – Cost and Life Expectancies for Each Alternative Table...................................... 118 Figure C.12 – Remediation Methods for Different Distresses Table. ........................................ 119 Figure C.13 – Decision Tree....................................................................................................... 120 Figure C.14 – LCCA Table......................................................................................................... 121 Figure C.15a – Combination of Trucks as Percentage of AADT. .............................................. 122 Figure C.15b – Truck Factor....................................................................................................... 122 Figure C.15c – Lane Distribution Factor. ................................................................................... 123 Figure C.16 – Common Distress Sheet for Shoving/Corrugation. ............................................. 124 Figure C.17 – Common Remediation Strategies for Microsurfacing. ........................................ 125
1
ACKNOWLEDGMENTS
It is a pleasure to thank those who made this thesis possible. First and foremost I offer
my sincerest gratitude to my advisor, Dr Soheil Nazarian, who has supported me through my
thesis with his patience and knowledge while allowing me the room to work in the Center for
Transportation Infrastructure Systems (CTIS) in a funded research project for the Texas
Department of Transportation, which was used as the topic of my thesis. My sincere gratitude to
Dr. Vivek Tandon and Dr. Peter Golding for serving as committee members.
I would like to give my sincere appreciation to Mr. Imad Abdallah, associate director of
CTIS, for his guidance through the development of the research project and special thanks to
Tania Ramirez for her participation and support.
I would like to thank my family that always encouraged me and supported me throughout
all my studies. I would also like to thank my friends and co-workers, Manuel Celaya, Dr. Deren
Yuan, Dante Mejia, Samuel Franco, Monica Jurado, Hector Hernandez, Enrique Portillo,
Shahram Misaghi, and Sara Montazeri.
2
CHAPTER 1: INTRODUCTION
1.1 BACKGROUND
Rural intersections originally constructed with thin untreated flexible base and hot mix or
a two-course surface treatment tend to experience severe pushing, shoving and rutting. These
failures cause an extremely rough surface that can cause damage to small vehicles and
potentially cause motorists to lose control of their vehicles. These distresses almost always
result in complete failure of the existing pavement that must be repaired several times during the
life of the roadway by maintenance forces. In most cases, pavements constructed with the same
materials and cross-sections adjacent to the intersection perform adequately.
The sources of and solutions for failure of the intersections in urban areas are well
researched and a number of solutions (such as full-depth concrete slabs, white topping, high
quality hot mix asphalt) have been implemented. For example, the National Asphalt Pavement
Association (NAPA) and the American Concrete Pavement Association (ACPA) have several
documents and training materials available for this purpose. Little attention has been focused
toward the rural low-volume road intersections in the US. A vast body of knowledge is available
from work done in other countries (e.g., Africa, Southeast Asia, Australia and New Zealand)
where the majority of their highway networks are either unpaved or are covered with thin surface
treatment. The primary motivation for reconstruction or rehabilitation of the urban high-volume
intersections is the speed of the operation to minimize the road closure, and the economy of the
solution is of the secondary consideration. However, to develop implementable solutions for the
rural intersections, the economy of the solution plays a primary role. The primary goal of this
project is to provide solutions that can be readily and economically carried out considering the
location of the project, the construction practices, and the type of potential or actual damage at
the intersections.
3
Since the sources of excessive distresses at the intersections and their possible solutions
are diverse, an easy-to-use excel program is proposed to incorporate the knowledge gained. The
program will provide step-by-step guidance on the process of identifying the source of the
problem, and selecting the best cost-effective alternative to mitigate the problem. The body of
evidence from other countries with vast network of low-volume roads indicates that the most
economical and effective solutions are those that strengthen the shallow subgrade or base instead
of adding layers of hot mix or concrete.
1.1.1 Low-volume Roads
Most roads in rural areas are low volume roads. A road is considered low volume by
AASHTO (2001) when subjected to an Average Daily Traffic (ADT) of less than 400 vehicles
and are characterized by lower speed limits. While TxDOT (2006) classification for low volume
road is where average daily traffic (ADT) is less than 1,000 vehicles per day (vpd) and
cumulative ESALs are less than 500,000 for a design period of 20 years.
A well planned, located, designed, constructed, and maintained low-volume road system
is essential for community development, flow of goods and services between communities, and
resource management activities (Keller and Sherar, 2003). Such roads are necessary to serve the
people in rural areas, allow the flow of products and services, facilitating commerce, and
improving development.
1.1.2 Traffic
Traffic load, especially from truck traffic, is a major parameter in the development of
rutting and fatigue cracking within the pavement. Overloaded trucks cause a disproportionate
amount of damage to the pavement structure, accelerating such deterioration (SADC, 1999). At
high stress locations, such as intersections, the braking and accelerating of vehicles increase the
damage to the pavement structure, leading to more significant permanent deformation and
fatigue cracking.
4
Several factors that resulted in increased rural truck traffic in Texas were identified and
discussed by Prozzi et al. (2004). These factors include:
• Agricultural industrialization resulting in fewer but larger farms and the trend toward
moving products between specialized operations predominantly by trucks;
• Increases in the physical sizes of agricultural equipment and the trend toward joint
ownership or the lease of large and expensive pieces of farm equipment or
outsourcing these services, resulting in increased movements on rural roads;
• Economic revival of the oil industry, resulting in relatively short but high-volume
“heavy” movements;
• House Bill 2060 that allows the trucking industry to purchase permits at a nominal fee
that allow 84,000-lb vehicles (gross vehicle weight) to traverse roads posted for
58,240 lb (gross vehicle weight);
• Location of large distribution centers of retail chains, such as Wal-Mart, HEB, and
Target, in rural counties, where land is comparatively inexpensive and major
highways provide access to major metropolitan markets;
• Location of landfill sites in western and northern Texas, which have raised concerns
about pavement rutting caused by overloaded garbage trucks;
• Dramatic increases in truck traffic resulting from the North American Free Trade
Agreement (NAFTA) that traverse a number of rural counties in Texas; and
• The abandonment of approximately 2,400 miles of rail track in Texas, following the
Staggers Act, which has decreased the potential for large Class I railroads to service
rural shippers, resulting in a large number of bulk commodities being moved on rural
roads.
The recent popularity of harvesting wind energy by constructing wind farms, also contributes to
this problem.
5
1.2 OBJECTIVES
The basic objective of this thesis is to accumulate the background information necessary
to develop a guide as a decision tool for pavement and maintenance engineers involved in the
design, maintenance and rehabilitation of low-volume road intersections. Based on this
background, the goals in this project are to achieve the following items:
1. Document the types of distress that are present in the field throughout Texas through
surveys and site visits.
2. Categorize the sources and layers that contribute to the damage at intersections.
3. Develop maintenance and rehabilitation guidelines for intersections with problems
4. Develop (minimum) pavement design for rural and urban intersections, and
5. Develop draft specifications for flexible pavement construction for rural intersections.
1.3 SCOPE OF STUDY
The ultimate objective of this research is to establish a new guide that would hopefully
provide the following information to pavement engineers:
1. Identify most prevailing distresses at an intersection, provide the source of the problem
and which layer of the pavement structure is failing;
2. Propose most appropriate rehabilitation and/or maintenance procedures, to repair and
prevent future failure of the pavement structure
3. Create an interactive design program to guide users through distress identification,
remediation selection, and design procedures for low volume road intersections;
4. Provide feasible design alternatives and remediation strategies to minimize cost without
compromise performance.
The specific scope of work for this thesis is to create a program that will serve as a
preliminary guide as a step in the process of developing the final interactive design program.
6
1.4 ORGANIZATION OF THESIS
Chapter Two contains a substantial literature review with work done on this matter
throughout the United States and the rest of the world. Characteristics and mechanisms of the
most common types of distresses of asphalt pavements and promising remediation strategies for
such problems at different layers of the structure are described. Current flexible pavement
design software is described and their advantages and limitations are identified. And finally
different methods of cost analysis are explained, compared, and discussed.
Chapter Three describes the overall research approach. The results of district survey
conducted at the beginning of this research are analyzed. The most prevailing low-volume road
intersection distresses and their causes are identified. The survey also collected the different
remediation methods utilized by Texas districts and their effectiveness. The input data for the
design and methodology are also presented.
Chapter Four provides a thorough pavement analysis of an intersection in the Texas
district of Atlanta. The intersection of SH155 and SH49 was examined using both destructive
and Non-Destructive Testing (NDT). A Visual Condition Survey was performed and Cores were
extracted from strategic locations. Falling Weight Deflectometer and Ground Penetrating Radar
was performed for both roads. Results obtained from Laboratory testing on the cores, FWD, and
GPR are summarized, analyzed and discussed. Laboratory results from the cores, and the
interpretation of deflection and radar data is summarized. Deep interpretation of the results
allowed generating conclusions on the type and source of the problem.
Chapter Five includes a preliminary utility of the excel sheet developed to assist in the
selection of remediation strategies. The site analyzed in Chapter 4 is evaluated in the
preliminary guide for the selection of a more cost-effective remediation strategy. Life cycle cost
analysis results are discussed for the repair alternatives.
Chapter Seven includes a summary of findings, conclusions, future work ahead and
recommendations for future research.
7
CHAPTER 2: REVIEW OF LITERATURE
2.1 OVERVIEW OF ROAD INTERSECTION CONDITIONS
A vast majority of the TxDOT highway system consists of secondary roads that are
constructed with thin pavement structures and thin hot mix asphalt surface or two-course surface
treatment. This network of low-volume roads has served the public well, and for the most part,
performs satisfactorily with periodic maintenance. One of the weakest links in this network is
the performance of the pavement at the intersections. Severe permanent deformation (pushing,
shoving and rutting) have been reported at intersections of some of these low-volume roads
while pavement sections constructed with the same materials adjacent to the intersection perform
adequately. These failures occur because of the higher severity of loads exerted to the pavement
at the intersections.
2.2 COMMON TYPES OF DISTRESS ON ASPHALT PAVEMENTS
2.2.1 Rutting
Rutting is defined as the longitudinal permanent deformation or plastic movement of the
asphalt pavement under the action of repeated loadings over the wheel path. Rutting is usually
caused by the densification and shearing of the different pavement layers. It is visually identified
by the depression in the pavement surface along the wheel paths. Even though visible on
pavement surface rutting may occur on any of the layers.
Rutting is a serious safety issue for drivers. When water accumulates in the ruts, there is
a potential for hydroplaning. The hydroplaning phenomenon consists of the buildup of a thin
layer of water between the pavement and the tire and results in the tire losing contact with the
surface, with the consequent loss of steering control (Yoder and Witczak, 1975).
Three main mechanisms lead to the following three types of rutting: Structural Rutting,
Instability Rutting and Surface/Ware Rutting. It is important to differentiate between these three
types of rutting and their potential causes. Different mechanisms lead to a variation in visual
8
characteristics of rutting. According to Fang (2001), shapes of transverse surface profiles differ
between failures in the HMA surface mixtures and failures in the underlying support layers.
2.2.1.1 Structural Rutting
The deformation of one or more layers underlying the HMA layer results in structural
rutting. Base and/or subgrade materials are unable to sustain the load stresses resulting in
depressions and lack of support to the superior layers, manifesting on surface rutting.
A cross sectional diagram of structural rutting is shown in Figure 2.1. Structural rutting
can be visually identified rather easily. Two main characteristics distinguish structural rutting
from other modes of rutting. Structural ruts are wide and do not have humps on their sides as
compared with instability rutting described later.
Figure 2.1: Structural Rutting on Asphalt Pavements (Federation of Canadian Municipalities and Canadian National Research Council, 2003).
The surface deformation is dependent on which of the layers is failing to support the load.
The visual characteristics will be different when the subgrade is failing as compared to the base.
Figure 2.2 illustrates and compares the difference between the surface deformation profiles due
to base and subgrade failures. When the base is failing, a small hump will be visible at the
surface in the middle of the two wheel paths, while the deformation due to subgrade failure will
have no humps at all with a wider wheel path depression (Fang, 2001).
9
a) Base Failure b) Subgrade Failure
Figure 2.2: Surface Deformation Due to Base and Subgrade Failure. (Fang, 2001)
Inadequate design, poor construction, and improper material specification in asphalt
pavement systems generally cause structural rutting. Traffic conditions, weak substructure, or
even poor drainage are essential parameters in pavement design. Miss-estimation of these
parameters leads to inadequate design and affect the pavement system which could induce
structural rutting.
2.2.1.2 Instability Rutting
Instability rutting or plastic flow is the type of rutting that is due to inadequate HMA mix
design rather than the structural design. Epps (1990) reported that the shear deformation, rather
than densification, is the primary rutting mechanism in HMA surface mixtures when the
supporting layers are reasonably stiff. This kind of rutting is visually recognized by the humps
formed on the sides of the rut as shown in Figure 2.3.
Figure 2.3: Instability or Plastic Flow on Asphalt Pavements (Federation of Canadian Municipalities and Canadian National Research Council 2003).
10
This type of distress is more visible in slow trafficked area of the pavement such as
intersections which represent a variance in the loading conditions applied to the pavement.
Braking, accelerating, turning, standing, and slow moving stresses at intersections induce
instability rutting. It may also be contributed by factors such as:
• High pavement temperatures.
• Improper materials.
• Rounded aggregates.
• Too much binder and/or filler.
• Insufficient or too high air voids
According to Colorado Department of Transportation Pavement Design Guide (CDOT,
2009), during warm summer months the sun radiation and the exhaust of the slow/standing
vehicles raise the pavement temperature. At higher temperatures a reduction in the HMA
stiffness occurs, which may induce instability rutting in the HMA layer. Dripping engine oil and
other vehicle fluids are also concentrated at intersections and tend to soften the asphalt (CDOT,
2009). At intersections, stopped and slow moving traffic allow exhaust to elevate asphalt surface
temperatures even higher. A properly designed mixture with a stiffer asphalt binder and strong
aggregate structure will resist plastic deformation of the hot mix asphalt pavement.
2.2.1.2 Surface/Wear Rutting
Wear rutting is the consolidation in the wheel paths of the HMA layer due to insufficient
compaction effort which is usually reflected in not achieving the target density. Consequently
additional compaction to the asphalt layer is generated by vehicle loading without any base/
subbase yielding or the formation of HMA humps as seen in Figure 2.4. According to CDOT
(2009) the following list of factors contributes to this type of rutting:
• Insufficient compacting effort within the lower base layers
• Not enough roller passes while paving
11
Figure 2.4: Wear Rutting on Asphalt Pavements (Federation of Canadian Municipalities and Canadian National Research Council 2003).
• HMA cooling before target density
• Asphalt moisture or dust
• Low asphalt content in the mix
• Lack of cohesion in the mix (tender mix, gradation problem)
Wear rutting is also the result of chains and studded tires wearing away the pavement surface
during winter season. This problem is not common in Texas.
2.2.2 Shoving
Shoving of an asphalt concrete pavement is defined as the longitudinal surface
displacement of the HMA. Shoving is usually caused by an unstable asphalt layer that is not
strong enough to resist horizontal stresses. Acceleration and deceleration of vehicles represent a
continuous load in the same direction that generally causes shoving as shown in Figure 2.5.
Excess binder in the mix, mistakes in the gradation, and erroneous temperature during
compaction are parameters that cause a weak asphalt mixture. These potential problems along
with poor bonding between the HMA and the underlying layer decrease the resistance to
horizontal stresses leading to shoving. Shoving can be easily identified by distortion of pavement
markings, and vertical displacements (dips and bumps). In many cases shoving is manifested
12
Figure 2.5: Shoving on Asphalt Pavements.
with a large “bow wave” in front of the braking section or areas where HMA abuts a rigid object
such as utilities. Shoving affects ride quality and may represent a safety hazard.
2.2.3 Fatigue Cracking
Fatigue in asphalt pavement manifests itself in the form of cracking from repeated traffic
loading (Suo and Wong, 2007). Three main factors that affect the initiation and propagation of
fatigue cracking are the mix design, pavement structure, and construction procedures. The main
visual characteristics of fatigue cracking are the interconnection of cracks in a chicken wire/
alligator pattern as seen on Figure 2.6.
Fatigue cracking is an important mechanism in the deterioration of asphalt pavements
because of the harmful effect this cracking has on the stiffness and strength of pavement.
Cracking allows water to percolate to the underlying layers, weakening the support and therefore
accelerating permanent deformation of the pavement sections.
2.2.4 Other Distresses
The dominant distresses at intersections are rutting, shoving and fatigue cracking,
however other distresses may manifest at the intersections. The sources of the dominant
distresses can also generate additional distresses and the distresses themselves can represent a
source of other distresses. Such is the case of moderate to high severity fatigue cracked areas,
13
Figure 2.6: Shoving on Asphalt Pavements.
where the interconnected cracks form pieces that when moved while subjected to traffic leave a
Pothole behind. Another surface defects such as bleeding, raveling and polished aggregates are
distresses present at intersections which according to the Long-Term Pavement Performance
Program (2005) are potential mixture related performance problems.
2.3 REMEDIATION STRATEGIES OF ASPHALT PAVEMENT AT INTERSECTIONS
The sources of and solutions for failure of the intersections in urban areas are well
researched and a number of solutions (e.g., full-depth concrete slabs, white-topping, high quality
HMA overlay etc.) have been implemented. For example, the National Asphalt Pavement
Association (NAPA) and the American Concrete Pavement Association (ACPA) have several
documents and training materials available for this purpose. On the other hand, less attention has
been focused intersection on the rural low-volume road in the US. In many countries in Africa
and Southeast Asia, and in Australia and New Zealand the majority of their highway networks
are either unpaved or are only covered with surface treatment. Much can be learned from their
operations and incorporated into this research. In this section a review of international strategies
is presented. The strategies and operations from this collection of work will help provide the
initial framework for developing implementable solutions for the rural.
14
2.3.1 Current TxDOT Specifications for Flexible Pavement Rehabilitation
According to the TxDOT Pavement Design Guide (2006) developing a rehabilitation
design generally requires extensive investigation into the condition of the existing pavement
structure, performance history, and laboratory testing of materials to establish suitability of
existing and proposed materials for use in the rehabilitation design. The field investigation
requires a deflection survey, drainage survey, and perhaps additional nondestructive testing
(NDT) surveys such as ground penetrating radar (GPR), dynamic cone penetrometer (DCP), and
seismic. Examination of multi-year Pavement Management Information System (PMIS) distress
and ride data can show the performance related issues. Once these preliminary surveys are
conducted, locations for material sampling can be established. In addition, for projects where
full-depth reclamation is being considered, samples of the structure should be taken at intervals
not to exceed 0.5-mi. These samples are evaluated in the lab to verify field survey conclusions
and establish basic properties necessary to quantify moisture susceptibility, stabilizer
compatibility, blending requirements, etc. The preferred rehabilitation strategy should:
• be cost-effectiveness
• address the repair of the specific problems of the existing pavement
• prevent of future problems, and
• meet all existing constraints of the project.
TxDOT currently does not have a specific strategy to approach problems with flexible
pavement at intersections; therefore such problems have been approached with regular road
procedures, even though intersections represent a different situation. The outcome of this
research study is to provide at minimum a handbook designed for maintenance personnel
showing “best practices” for maintaining flexible pavements at intersections and an expert
system that allows for selecting the optimal remediation strategy at intersections.
15
2.3.2 Asphalt Institute
The Asphalt Institute (AI) published a set of articles named “Intersection Strategy” (e.g.,
Walker and Buncher, 1999). These articles include guidelines to diagnose the sources of the
pavement distress and to select the proper methods to repair them. Different agencies have
adopted the AI strategies and/or developed guidelines that are similar to them. The Plant Mix
Asphalt Industry of Kentucky (PAIKY), Asphalt Pavement Alliance (APA), Maryland Asphalt
Association and the National Asphalt Pavement Association (NAPA) are among the agencies
that follow the AI strategy. States such as Oregon have also adopted the strategies promoted by
the AI in their pavement design guides. Canada’s strategy goes along with the Asphalt
Institute’s as reflected in their 2003 publication entitled “Rut Mitigation Techniques at
Intersections.” The intersection strategy consists of the following four steps to minimize
distresses and rehabilitate intersections.
1. Evaluate Performance Problems and Causes
2. Ensure Pavement is Structurally Adequate
3. Select appropriate Materials Selection and Mix Designs
4. Adapt proper Pavement Construction Techniques and Selection of Rehabilitation Method
Each step is described below.
2.3.2.1 Evaluate Performance Problems and Causes
The main concern at HMA intersections is the presence of rutting owed to a weak mix or
higher than normal stress conditions. Identification of rutting problems at intersections can be
through user complaints, staff inspections, or visual and/or measured monitoring. A forensic
investigation is the key to find the root of the problem. It is important to monitor the pavement
surface condition to establish the rate of deterioration.
A visual inspection of the pavement surface conditions should be the first step to initiate
a forensic study. It should be performed by a pavement engineer who has experience in
16
identifying distresses in pavements. It is important that the location (lane), extent (distance the
rutting extends before and after the intersection), and severity of the rutting are established.
After identifying the severity, an evaluation of the causes should be carried out. The
evaluation of any roadway that may need rehabilitation may include:
• Deflection testing (FWD, Dynaflect, or Benkelman)
• Coring pavement and subgrade samples
• Thickness measurements for all layers of the pavement
• Determination of material properties of subgrade, granular base and asphalt concrete
• A review of the construction and maintenance information.
The findings are then analyzed to determine the type (or types) of rutting that has
occurred and its causes, to determine the most appropriate rut mitigation strategy.
The analysis of the pavement structure will allow for determining the type or types of
distresses present at the intersection, and help choosing a rehabilitation strategy from the
following alternatives:
• Pavement preservation (e.g., with low severity instability rutting);
• Pavement overlay (e.g., with medium severity instability rutting);
• Pavement rehabilitation (e.g., with high severity instability rutting); or
• Pavement reconstruction (e.g., with pavement structural rutting).
A life cycle cost analysis should be performed to select the most cost-effective method.
2.3.2.2 Ensure Pavement is Structurally Adequate
A proper structural design must take into account the subgrade strength, base thickness
and traffic. The middle of the intersection receives loading from several approaches and should
be considered in the traffic evaluation. Overlaid, rehabilitated, or reconstructed existing
pavements must have structural adequacy for current and anticipated future traffic loads
(ESALs). For existing pavements, the structural capacity of the in-place materials must be
checked, and any failed or weak areas removed or replaced (Buncher, 2002; Walker and
17
Buncher, 1999). A new design has to be carried out. Replacing the asphalt with the same mix
design or paving on top of existing failed pavement will most likely result in recurring failure.
2.3.2.3 Appropriate Materials Selection and Mix Designs for HMA
The long term performance of an asphalt pavement is dependent on the stiffness of the
asphalt binder and the characteristics of the aggregates. The binder stiffness plays a critical role
in the permanent deformation resistance of an asphalt pavement. So is the shape and strength of
the aggregates, which combined represent the skeleton providing strength from stone-to-stone
contact. The binder should be stiff enough to prevent rutting while the aggregate must be
angular to ensure a better aggregate interlocking and bonding than rounded aggregates.
The use of the Superpave’s Performance Grade (PG) binder system is highly
recommended. Table 2.1 indicates the Superpave binder selection adjustments for different
ESAL and loading rates. The PG system selects a binder based on its ability to perform at the
temperatures to which the pavement will be subjected. It is a common practice for slow moving
design loads to “bump up” the binder one grade, and for standing loads two grades. According
to previous experiences at numerous sites across the US, PG 76-XXs should perform well at
intersections (Buncher, 2002).
The aggregate structure carries the load and the shearing forces while the binder holds it
together. A proper aggregate selection and gradation is essential. A strong, coarse, and angular
aggregate with multiple faces will provide more internal friction and create an aggregate matrix
that will resist better the shearing forces that lead to rutting. The amount of rounded aggregates
should be limited.
A rut-resistance mixture that has proven to be of great reliability for intersections is Stone
Matrix Asphalt. This gap-graded mixture relies on stone-to-stone contact and can be a good
option to be applied as a base mixture.
18
Table 2.1: Superpave Binder (PGAC) Selection Adjustments (Bumping) for Design ESALs and Loading Rate.
High Temperature Grade Increase in 6 °C Grade Equivalents Heavy Traffic (Trucks and/or Buses) Loading Rate (Speed)
Design ESALs Million
Standing < 20 km/hr Slow 20 to 70 km/hr Standard > 70 km/hr < 0.3 - - -
0.3 - < 3 2 1 - 3 – 10 2 1 -
10 - < 30 2 1 - > 30 2 1 1
2.3.2.3 Proper Pavement Construction Techniques
The performance of any pavement is highly dependent on the pavement construction
techniques followed, and the quality of construction achieved. Proper construction techniques
include the following.
• Prepare the substrate properly. Thoroughly clean old or milled surfaces, remove any old
patches or thin asphalt concrete areas that may debond, and uniformly tack prepared
surfaces at the appropriate application rate.
• Produce, place, and compact HMA at appropriate temperatures
• Avoid segregation with proper aggregate stockpiling, and hot-mix asphalt production,
transportation, and placement techniques.
• Place a uniform and smooth mat.
• Construct transverse and longitudinal joints properly for durability and to prevent the
ingress of water.
• Achieve the compaction (density) requirements.
• Follow an appropriate quality control plan to achieve the proper construction techniques
and overall quality.
19
2.3.2.3 Selection of Rehabilitation Method
The rehabilitation method selection for a rutting problem at an intersection should be
based on a life cycle cost comparison analysis. Any pavement used for rehabilitation should
follow the recommendations above.
Mill and Overlay with Asphalt Concrete
Resurfacing is the most common rehabilitation method for flexible and composite
pavements. It is necessary to mill a superficial portion of rutted asphalt pavement, and then
replace a surface layer of the pavement with rut-resistant HMA. An intimately bonded interface
between the milled surface and the HMA overlay has to be ensured. It has to be clean, any loose
material has to be removed a properly tack coat needs to be placed in between.
Rut Filling Using Spray Patching, Thin Overlays, or Micro-Surfacing
On wear rutting and low severity instability rutting, the wheel path ruts can be filled by
spray patching, or by micro-surfacing, and/or tacking, as necessary, before the HMA
overlay/micro-surfacing. Spray patching is appropriate for lower volume, rural or surface-
treated pavements. Rut filling should only be viewed as a relatively short-term mitigation
measure.
Grinding and Precision Milling
This procedure can be used to restore the surface texture and profile of pavement, when
medium severity instability rutting is present. It consists of removing the rutted surface of the
concrete to the rutting depth. It offers a short-term solution to instability rutting.
White-topping (Conventional and Concrete Inlay)
White-topping is defined as the construction of a new Portland Cement Concrete (PCC)
over an existing flexible pavement. White-topping can be a technically and cost-advantageous
rehabilitation alternative for badly deteriorated asphalt concrete at intersections, particularly for
flexible pavements exhibiting instability, rutting, shoving, and alligator cracking (Smith et al,
2002).
20
The interface between the old asphalt pavement and the new PCC overlay may be a
milled surface, a HMA leveling course, or direct placement (no treatment at all). Conventional
white-topping is generally suitable for the traffic loading associated with urban road
intersections. PCC is designed as if it was on a treated base course.
Ultra-Thin White-topping
A thin layer of PCC is placed over a prepared distressed flexible pavement. The
deteriorated asphalt concrete surface is cold milled to enhance the bond between the PCC and
asphalt concrete. Ultra-thin white-topping is intended for parking areas, urban streets, bus bays,
and intersection flexible pavements where instability rutting is a problem, but no other
significant deterioration is present (ACPA, 1998; Smith et al., 2002). The UTW is generally
intended for flexible pavements subject to lower volumes of heavy traffic (Smith et al., 2002).
Thin Composite White-topping (TCW)
TCW is defined as “a concrete overlay intentionally bonded to an existing asphalt
pavement to create a composite pavement section. Joints are spaced at close intervals to reduce
stresses in the concrete overlay (Cole et al, 1997). This is an emerging technology and it is
intended for high volume roadways. Pavement thickness is based on engineering judgment and
performance of previously placed TCW pavement installations.
Roller Compacted Concrete (RCC)
Roller compacted concrete is a very dry zero-slump cement-aggregate mixture with
supplementary cementing materials so that it remains stable for compaction by vibratory rollers
like those used for asphalt pavement compaction.. Asphalt pavement placed over the RCC may
provide a smoother ride for the driving public.
Hot in Place Recycling (HIR)
The Colorado DOT Pavement Design Manual (2009) indicates that the HIR should be
used to fix surface distresses when the cause of the problem is not structural, but merely from the
upper asphalt layer, such as cracking and minor rutting. The process is performed by heating and
21
mixing equipment which preheats the asphalt to soften it and then mills it so it can be mixed with
binder, new aggregates, or any other additives to be finally re-compacted. The main benefit from
this process is the conservation of both materials and energy by recycling on site.
Cold in Place Recycling (CIR)
CIR is defined as a rehabilitation technique in which the existing pavement materials are
reused in place. The CIR process usually uses 100% of the reclaimed asphalt pavement (RAP)
without the application of heat for the recycling process. CIR can be useful in eliminating
rutting within a range of 2 to 4in. in depth, eliminate potholes, rough areas and restore the design
profile. Although cold recycled mixes can produce stable surfaces, a wearing surface over the
recycled mix is normally required.
2.3.3 Canada
The Federation of Canadian Municipalities and Canadian National Research Council
(2003) have developed a comprehensive guideline for rehabilitation of intersections. Figure 2.7
provides the flowchart of their activities to address the instability rutting at intersections. The
flowchart of activities displays how important is the communication and feedback between the
different levels of design. The process starts with analyzing the pavement performance by
identifying the type of distresses and the sources of the problem. With loops through the design
procedures it aims to ensure structure adequacy and meanwhile trying different rehabilitation
methods starting from the most economical targeting cost-effectiveness.
2.3.4 Colorado Department of Transportation (CDOT)
The CDOT present a slight variation on addressing strategies at intersections. The
Colorado Pavement Design Manual (2009) considers the intersections separately since they hold
merged traffic directions over a same pavement section. As a result, the number of vehicles from
each of the intersecting roads is accumulated and thereby exceeding the traffic design of each of
the roads. Another factor they consider is the drainage within intersections, since improper
drainage can lead to moisture damaging the pavement and saturating the so underlying base and
22
Figure 2.7: Flowchart of Activities for Mitigating Intersection Rutting.
23
subgrade layers leading to lack of support and thereby deformation of the complete pavement
structure. The key items used by CDOT for proper scoping of the projects are the following:
• Identify the problem with existing intersection.
• Remove enough pavement layers to find the problem.
• Design and reconstruct with a high performance HMA mix especially formulated.
CDOT designs asphalt pavements for a period of at least 20 years and for restoration and
resurfacing of 10 years. General considerations by CDOT to design a HMA intersection include
the following:
• Heavy truck and high volume traffic intersections require extra considerations in their
design and construction. High performance intersection design should be considered
when 20-year traffic loading of the two traffic streams adds up to one million ESALs or
more.
• Intersection pavements suffer from slow traffic and sharp turns, and such factors must be
included in the design. The road is also vulnerable to deceleration and acceleration of
vehicles approaching an intersection. A stronger transition pavement should be applied
before and after every intersection. If there is two-way traffic, the transition should
extend 300 ft in both directions. When one-way traffic, transition should be at least 300
ft on the deceleration side and 100 ft on the acceleration side of the intersection.
• A PG 76-28 binder is suggested by the CDOT for intersection pavements. “Bumping”
binder grades would improve performance of asphalt. Superpave procedure to select
binder grade for asphalt intersections is recommended.
2.3.5 Australia
The Australian Asphalt Pavement Association (AAPA, 1999) provides an advisory note
entitled “Bituminous Surfacing for Intersections on Light and Medium Duty Flexible
Pavements” as a guide to utilize spray seal (chip seal in the US) and other bituminous treatments
over unbound and lightly bound granular pavements, especially in rural areas. A spray seal is
24
done by spraying a layer of binder on top of a damaged road surface and then covering it with
aggregates. The binder waterproofs the pavement while the aggregate provide extra damage
protection to the pavement. Sprayed seals provide an effective and economical resurfacing
alternative in a large number of situations, but the turning and braking of heavy vehicles at
intersections grind away the surface aggregate inducing the bleeding of the seal.
The performance of the spray seals can be improved by different methods, but
supplementing the spray seal with a thin layer of HMA can improve smoothness and appearance,
representing a longer term cheaper alternative. Performance of spray seals for high stress
situations can be enhanced by:
• Polymer Modified Binders (PMB): also called High Stress Seals (HSS) to boost binder
cohesion, toughness and improve temperature resistance.
• Multiple applications of binder and aggregate to produce a stronger spray seal. They
recommend two applications of aggregates, the second one having predominantly
aggregates half the size of the first one. This will allow the smaller aggregate to be
accommodated within the voids left by the larger aggregates, providing a better clutch
and therefore a stronger structure against vehicle shearing forces.
• Multiple application of aggregate (“racked in” or “dry lock” techniques) by light
application of a small size aggregate (0.2in.) over a coarser aggregate sprayed seal in
order to prevent the coarse aggregates from rolling away during seal compaction.
Guidelines for asphalt surfacing for intersections and roundabouts are as follows. For
lightly trafficked pavements, the surface of the pavement has to be primed. For clean and in
good condition primed surfaces tack coat may not be necessary, so it may be either reduced or
discarded. Since a dense surface finish and durability are the main requirement, small aggregate
sizes in a fine texture and workable mixes are usually used.
For medium trafficked pavements a common alternative is the construction of a sprayed
seal pavement with asphalt surfacing in areas where vehicles turn, such as intersections, medians
and roundabouts. The granular pavement should be surfaced with a prime seal or prime and sand
25
but first they should be allowed to dry to a moisture content no greater than 70% of optimum. If
possible, before any asphalt surfacing is performed, the seal should be also given some time to
allow compaction under traffic and evaporation of cutters. High level of cutters may lead to
bleeding of the asphalt surfacing. Time will also help to identify the surface weaknesses of the
pavement. Mix design has to be developed according to the road requirements. In Australia 4 or
6 in. thick dense graded asphalt mixes are used for most medium to heavy traffic conditions.
2.3.6 New Zealand
Transit New Zealand (2004) has a supplementary document to the Austroads (The
National Association of Road Transport and Traffic Authorities in Australia) called “Pavement
Design – A Guide to the Structural Design of Road Pavements” which considers the high lateral
stresses induced at intersection and thereby requires attention while designing and constructing
all layers in a pavement structure. Intersections are exposed to loading from different directions
and this parameter should be considered in the design. Intersection must extend into the
approach road by an appropriate distance.
For structural adequacy, the thickness and configuration of each layer has to satisfy the
critical strain criteria. In case of a flexible pavement at the intersection, elastic deflection (based
on the Benkelman Beam) must not exceed an acceptable level of approximately 1mm to prevent
fatigue cracking.
The upper pavement materials must have high shear strengths to resist the high levels of
shear stress applied on the pavement surface as a result of vehicles slowing down, accelerating,
breaking, and cornering at intersections. The use of structural asphalt, concrete or modified
aggregate materials should be considered. In New Zealand, Stone Matrix Asphalt (SMA) has
shown very good performance in terms of shear resistance and favorable surface properties.
2.3.7 Illinois DOT
The Illinois Department of Transportation Pavement Design (2002) contains specific
criteria to classify high-stress intersections and thereby select the required materials. High-stress
26
intersections are defined as those under stop control, either signal or sign that have one or more
of the following conditions:
• The approach grade on any stop-controlled leg of the intersection is greater than or equal
to 3.5%.
• The two-way average daily traffic (ADT) for multiple unit (MU) vehicles is greater than
or equal to 400 in rural areas or 800 in urban areas. For ramps and other one-way
facilities, one-half of this ADT criterion is recommended.
• The ADT for turning MU vehicles on any one leg of the intersection is greater than or
equal to 200 vehicles in rural areas or 400 vehicles in urban areas. This also applies to
sharp turning movements that are not under stop control.
The materials for intersection pavement are chosen depending on the existing pavement
and the traffic conditions at the location. Pavement types for high-stress intersections are limited
to either PCC; or Superpave AC with an Ndesign greater than 90. The pavement materials for
high-stress intersections have to be used for a minimum distance of 150 ft from the stop sign.
Such length may be extended if a traffic study indicates it. Complete reconstruction, instead of
resurfacing, of an existing distressed pavement at an intersection should be considered in case of
rutting and/or shoving.
Intersections not meeting the mentioned criteria are not considered high-stress
intersections. Still they can develop similar signs of permanent deformation as those on the
high-stress intersections. Non-high-stress intersections paved with PCC pavement may use PCC
for repair if the improvement consists of minor widening without resurfacing.
Non-high-stress intersections with asphalt pavement showing signs of permanent
deformation (rutting, shoving) should be examined to determine the source of the problem. An
evaluation of the complete structure must be performed to determine what material might be
inadequate. Such material has to be removed and replaced before any resurfacing. In cases that
the HMA mixtures seem to be stable but the problem persists, then an exception to the high-
27
stress intersections criteria should be considered. Example conditions which may allow
exceptions include:
• Lower urban ADT for MU vehicles if all are required to stop or if the approach speed is
greater than 40 mph;
• Lower urban and rural ADT for MU vehicles if the majority are fully loaded at
intersections near warehouse facilities, landfills, grain elevators, etc.;
• Demonstrated problems with shoving of a bituminous overlay related to tight turning
movements; and
• Including single unit (SU) trucks in the MU truck count where the SU vehicles are
primarily fully loaded hauling vehicles (e.g., grain trucks, concrete trucks, coal trucks).
2.3.8 Hot Mix Asphalt Mixtures for Nevada’s Intersections
The Nevada Department of Transportation (NDOT) uses a coarse dense graded HMA that
has successfully resisted rutting under normal highway traffic loading throughout the entire state.
However, the performance of the mixture at the intersection has been inadequate. Hajj et al.
(2007) developed specific requirements for hot mix asphalt mixtures for Nevada intersections.
In that study, Hajj evaluated the Asphalt Pavement Analyzer (APA), the Repeated Shear at
Constant Height (RSCH), and the repeated load triaxial test (RLT) as potential candidates for a
mix design test for intersection mixtures in addition to the triaxial compression strength test. He
recommended the following criteria to assess the permanent deformation for mixes placed at the
intersections and stopping areas:
• RSCH: maximum of 1.9% permanent shear strain at 158°F after 5,000 cycles.
• RLT: maximum of 2.0% permanent axial strain at 158°F after 12,000 cycles.
• APA: maximum of 0.06 in. at 140°F after 8,000 cycles.
28
2.3.9 National Center for Asphalt Technology (NCAT)
Kandhal (1998) conducted a field investigation to determine the cause of rutting at
intersections. A list of considerations to minimize permanent deformation proposed by Kandhal
is as follows:
• Lower Asphalt Content: Higher asphalt content is needed for improved fatigue life and
durability of the asphalt mix, but it tends to enhance the rutting and shoving problems.
The mix needs to be maximized for fatigue and permanent deformation through a
compromise.
• Coarser Gradation: Finer gradations or over-sanded mixes are more susceptible to
permanent deformation.
• Angular and Rough Textured Aggregate: This is especially applicable to the fine
aggregate fraction. Kalcheff and Tunicliff (1982) and Brown and Cross (1992) have
demonstrated that mixtures utilizing angular manufactured sand are more resistant to
permanent deformation than mixes produced with rounded or sub-rounded natural sand.
• Increased Air Void Content: Mixtures with low voids in the mineral aggregate (VMA)
and higher asphalt contents have a tendency to have very low air void contents after
densification by traffic. Such mixtures lose stability after reaching a critical compaction
level and start to rut and shove.
• Higher Viscosity Asphalt Binder: An asphalt binder with a high viscosity at 60°C will be
more resistant to horizontal thrust as far as plastic flow in a mix is concerned compared to
a low viscosity asphalt binder.
• Higher Fines Content: Increase in the minus 200 sieve fraction of the mix will tend to
stiffen (increase the viscosity) of the binder.
• Larger-Size Aggregate: At proper asphalt content larger-size aggregate (such as 19.5
mm) mix in the wearing course tends to be more resistant to permanent deformation.
• Reduced Overlay Thickness: If the existing pavement is structurally sound (for example,
Portland cement concrete), thicker asphalt mix overlays are unnecessary in the critical
29
areas like intersections. Thinner overlays (for example, binder course can be eliminated)
in these areas will minimize the problem.
• Improved Bond between Pavement Layers: A lack of good bond between the pavement
layers (especially in top 6in. of the pavement) can cause slippage due to horizontal thrust.
The following mixtures were recommended by Kandhal (1998) for use at intersections in hot
climates:
• 2 in. of Stone Matrix Asphalt (SMA) wearing course (nominal maximum size 12.5
mm)
• 2 in. of SMA binder course (nominal maximum size 19.0 mm)
• 2 in. of dense-graded large stone mix base course (nominal maximum size 25 mm)
2.4 REMEDIATION STRATEGIES CONSIDERING SUBSURFACE LAYERS OF PAVEMENTS
2.4.1 Base Layer
Structural inadequacy can be cause by subsurface layers as much as the HMA layer. It is
of utmost importance to identify the layer(s) that contribute to the excessive permanent
deformation of the intersections. If the base layer is the contributing factor to distress, treatment
of the top layer will not solve the problem. The remediation strategy needs to address the base
layer. Most of the time the under-designed base layer can be remedied by stabilization or
modifying the gradation.
Stabilization is achieved by adding proper percentage of additives such as cement, lime,
fly ash, bitumen, or combinations of these materials to the base. The selection of the type and
determination of the percentage of additive are dependent upon the soil classification and the
desired degree of improvement. Smaller amounts of additives are required to modify soil
properties such as workability and plasticity. Larger quantities of additives are used to
significantly improve the strength, stiffness and durability (Army TM 5-822-14, 1994).
Spreading and compaction are achieved by conventional means after the additive has been mixed
with the base. The most common improvements achieved through stabilization include:
30
• Reducing plasticity index
• Increasing durability and strength
• Reducing dust during construction
• Waterproofing the soil
• Conserving aggregate materials
• Reducing cost of construction
• Providing a temporary wearing surface
The South African “Guideline on Low-Volume Sealed Roads” (2003) considers that the
main objective of chemical stabilization is to enhance the suitability of locally available natural
materials for pavement construction, thereby avoiding the need to import other materials. This
can often lead to a more cost-effective alternative for construction.
The selection of stabilizer type depends on the type of material present and their location
in the pavement structure (Terrel et al., 1979). Table 2.2 provides varying stabilization methods
for different materials. Coarse and fine grained soils, as well as clays are suitable for
stabilization with Portland cement and lime-fly ash and lime. Typically, several criteria must be
followed for the selection of a stabilizer. Figure 2.8 demonstrates a basic flowchart used by
TxDOT for the selection of additive used for base treatment. Aside from the physical properties
of the soil, TxDOT also considers the goals of the treatment, mechanisms of additives, desired
engineering and material properties, design life, environmental conditions and economical
factors.
A simple mechanical stabilization alternative exercised in South Africa often satisfies the
specifications of a standard material. This alternative consists of blending two natural materials,
gravel with sand, to form a mechanically stable layer by lowering the PI and optimum moisture
content (OMC), and by improving the strength and the workability of the material.
31
Obtain samples of base material source in accordance with Tex-40-E. Perform material
testing required by Item 247 (Table 1) requirements.
Select initial additive(s) based on criteria: gradation, plasticity index, goals of treatment,
mechanisms of additives, desired engineering and material properties (strength, modulus, etc.),
design life, environmental conditions (drainage, water table, etc.), engineering economics (cost
savings vs. benefit).
Evaluate the overall improvement and durability of the enhanced engineering and material properties.
Perform mix design to determine the improvement of engineering properties at varying concentrations
of selected additive.
No treatment is required, unless additional strength and quality is specified for the project.
Select another additive(s) and repeat mix design.
Does the material meet Item 247 (Table 1)
requirements?
Do the improved properties meet the
min. project requirements?
Proceed with construction.
NO
YES
YES
NO
Figure 2.8: TxDOT Flowchart for Base Treatment (TxDOT, 2005a).
32
Table 2.2: Stabilization Methods for Different Soil Types (Terrel et al., 1979)
Soil Types Most Effective Stabilization Methods Coarse granular soil Mechanical blending, soil-asphalt, soil-cement, lime-fly ash
Fine granular soil Mechanical blending, Portland cement stabilization, lime-fly ash, soil-asphalt, chlorides
Clays of low plasticity Compaction, Portland cement stabilization, chemical waterproofers, lime modification
Clays of high plasticity Lime stabilization
A large variety of industry by-products and commercially produced additives is available
for use in pavement stabilization, such as:
• Air-cooled blast furnace slag
• By-product lime
• Fly ash
• Ground granulated blast furnace slag
• Reclaimed asphalt pavement
• Recycled concrete material
2.4.1.1 Full Depth Reclamation
Full depth reclamation (FDR) is a form of cold in-place recycling of flexible pavements.
During this procedure, the hot mix layer and a predetermined amount of the underlying base
course are pulverized simultaneously by special equipment. As a common practice, the two
materials are mixed with stabilizing agents described above. Depending on the severity of
structural problems of the original base course, additional virgin base material (add-rock) or RAP
is sometimes mixed with the pulverized materials. The result of this process is an entirely new
base material. Increasing shortages of virgin aggregate, rising fuel costs, as well as
environmental concerns have led to an increased utilization of FDR in many states and countries.
Recycling using the FDR process has many advantages which encompass a broad range
of engineering concerns, from improving the economics of the project to safeguarding the
environment. FDR facilitates complete reconstruction of a pavement system while utilizing all
33
or most of the existing material. The process allows for grade corrections and small adjustments
in road geometry, but more importantly, remedies structural pavement problems (Kearney and
Huffman, 1999). The ability to utilize almost 100% of the existing materials reduces project
costs associated with the transportation of virgin material to the site while concurrently
eliminating disposal costs of the old aggregates. Aside from the obvious economic benefits,
FDR addresses “deeper” pavement problems as well.
Cracking and other defects are sometimes caused by inadequate base materials in flexible
pavement systems. In these cases resurfacing of the road with another hot mix layer will not
solve the problem. FDR can be implemented on these roads to strengthen the base materials
(Kearney and Huffman, 1999). The new base that is formed from the combination of the
existing pavement and part or all of the base material along with a stabilizing agent is often times
stronger than the original materials. For this reason, roads that have undergone the FDR process
are often considered to be structurally sounder than the original flexible pavement.
Since the pulverization process reaches deep into the base material, changes in the profile
of the road are attainable during the FDR process. Epps (1990) states that significant pavement
structural improvements can be made in horizontal and vertical geometry and without shoulder
reconstruction. Old pavement profile, crown, and cross slope may be improved. This is possible
since the entire layer of flexible pavement as well as part of the base is taken up. The advantages
of FDR are not only limited to road improvements, it is also an environmentally sound choice for
pavement rehabilitation as well.
Some problem areas have also been associated with the use of FDR. No comprehensive
guidelines are currently in place that governs the implementation of the process. This has lead to
large variations in the results of such projects, even within the same State. Another concern with
FDR is the curing time required for strength gain. Curing time is a major factor in the decision
of when to let traffic back on that particular section of road. This in turn causes inconvenient
disruptions in traffic. However, advances in equipment used for FDR has helped streamline the
process so that road closures can be kept to a minimum (Epps, 1990). Also, the entire process is
34
susceptible to climactic conditions, especially when asphalt emulsions are used as a stabilizing
agent. Since the strength gain is dependent on the rate of moisture loss by the emulsion, it is not
recommended that the process be carried out on days when heavy rainfall is expected.
2.4.2 Subgrade Layer
Ideally the subgrade should be strong and stiff enough to prevent excessive rutting.
However, for fine-grained silt and clay soils, poor strength, high volumetric instability, and
freeze/thaw durability problems are predominant. For expansive soil the volumetric change may
be more severe and thus become a bigger challenge. The expansion action may result in
intolerable differential heaving of pavements. Common remediation methods can be categorized
into two groups: (1) to improve strength and (2) to minimize moisture variation. To improve soft
subgrade bearing capacity and strength, thicker layers of high-quality granular material may be
used on top of the problematic subgrade. In other instances, stabilization and geosynthetic
reinforcement can be used. The common strategies used to minimize moisture variations and
fluctuations as summarized by Raymond and Ismail (2003) include:
• Treat the soil with lime or other additives to reduce expansion in the presence of
moisture;
• Replace the material with a better material to a depth below which the seasonal moisture
content will remain nearly constant;
• Provide an overlaying structural section of sufficient thickness to counteract the
expansion pressure by surcharge;
• Stabilize the moisture content by minimize the access of water through surface and
subsurface drainage and use waterproof membrane such as rubberized asphalt membrane,
geosynthetics, put moisture barrier and/or remove nearby vegetations.
2.4.2.1 Admixture Stabilization
Admixture stabilization refers to mixing and blending a liquid, slurry, or powder with soil
to improve soil strength and stiffness properties. Lime stabilization is a widely used means of
35
chemically transforming unstable soils into structurally-sound construction foundations. Lime
stabilization creates a number of important engineering properties in soils, including improved
strength; improved resistance to fracture, fatigue, and permanent deformation; improved resilient
properties; reduced swelling; and resistance to the damaging effects of moisture. The most
substantial improvements in these properties are seen in moderately to highly plastic soils, such
as fat clays (Little et al., 2000). Little (1999) indicated that lime stabilization often induces a ten
fold stiffness increase over that of the untreated soil or aggregate. Croft (1967) found that the
addition of lime significantly reduces the swelling potential, liquid limit, plasticity index and
maximum dry density of the soil, and increases its optimum water content, shrinkage limit and
strength.
Cement has been found to be effective in stabilizing a wide variety of soils, including
granular materials, silts, and clays; byproducts such as slag and fly ash; and waste materials such
as pulverized bituminous pavements and crushed concrete. It is generally more effective and
economical to use it with granular soils due to the ease of pulverization and mixing and the
smaller quantities of cement required. Fine-grained soils of low to medium plasticity can also be
stabilized, but not as effectively as coarse-grained soils. If the PI exceeds about 30, cement
becomes difficult to mix with the soil. In these cases, lime can be added first to reduce the PI and
improve workability before adding the cement (Hicks, 2002). Addition of cement to clay soil
reduces the liquid limit, plasticity index and swelling potential and increases the shrinkage limit
and shear strength (Nelson and Miller, 1992).
Stabilization of soils and pavement bases with fly ash is an increasingly popular option
for design engineers. Fly ash decreases swell potential of expansive soils (Ferguson 1993, White
et al., 2005a, b). Soils can be treated with self-cementing fly ash to modify engineering
properties as well as produce rapid strength gain in unstable soils. Tests results show that fly ash
increases the compacted dry density and reduces the optimum moisture content (White et al.,
2005a). Fly ash can also dry wet soils effectively and provide an initial rapid strength gain,
which is useful during construction in wet, unstable ground conditions. Çoçka (2001) found that
36
plasticity index and swell potential decrease with increasing fly ash contents. Ferguson (1993)
noted that the decrease in plasticity and swell potential was generally less than that of lime
because fly ash did not provide as many calcium ions that modify the surface charge of clay
particles.
Lime and lime fly ash stabilized materials cure much slower than Portland cement
stabilized layers. As with strength properties, resilient properties of lime-soil mixtures are
sensitive to level of compaction and molding moisture content. Lime-stabilization may
substantially increase shear and tensile strengths. This strength increase provides a stiffer layer
with improved load distributing capabilities. However, as the stiffness of the layer increases
through the development of cohesion within the stabilized layer, the layer becomes more
susceptible to load-induced tensile stresses that can lead to fatigue failure unless proper design
steps are taken to reduce the potential of load induced damage. This is generally accomplished
by ensuring that the layer thicknesses are such as to insure the development of acceptable
flexural stresses within the stabilized layer. Typically the design parameter is the flexural tensile
stress ratio. Thompson (1966) determined that the indirect tensile strength of lime-soil mixtures
is approximately 0.13 times the unconfined compressive strength. Chou (1987) stated that the
flexural tensile strength of lime-soil mixtures is approximately 0.25 times the unconfined
compressive strength.
For sulfate rich soils, a phenomenon called sulfate-induced heave can happen that can
severely reduce the long-term strength and durability of stabilized soil. If the sulfate levels are
above 3000 ppm, further recommendations and guidelines can be found in TxDOT (2005b).
Puppala et al. (2003, 2004) studied the effectiveness of sulfate resistant stabilizers such as
cement Types I/II, V, lime mixed with fibers and Class F fly ash in providing better treatment of
sulfate rich soils. Test results indicate sulfate-resistant cement provided the most effective
treatment. The combined lime and fibers stabilization method provided the next best effective
treatment. The Class F fly ash treatment provided low-to-moderate strength improvements that
could be attributed to the low amounts of calcium present in this type of fly ash. On the other
37
hand, the fly ash stabilization method was more cost-effective than the other methods. Kota et
al. (1996) provide some suggestions to minimize the damage caused by sulfates and calcium-
based stabilizers such as double application of lime, use low calcium stabilizers (e.g. cement and
fly ash), use non-calcium stabilizers, geosynthetic soil reinforcement, stabilization of the top
with non-sulfate select fill, pretreatment with barium compounds, asphalt stabilization of the
sulfate bearing soils and compacting to lower densities.
Organic contents in the soil are another consideration when selecting stabilization
additives. Organic soil is a soil that would be classified as a clay or silt except that its liquid
limit after oven drying (dry sample preparation) is less than 75% of its liquid limit before oven
drying (wet sample preparation). If the organics content exceeds 1%, additional additive will
need to be added to counter the cationic exchange capacity of the organic material.
Although chemical stabilization has proven successful in increasing the strength of the
natural expansive soils by twenty to fifty times, and is widely used, situations arise where above
mentioned approaches cannot be used. For example, chemical stabilization cannot be used when
the temperature is below 40oF and in cases there are not enough time for curing before traffic is
routed back (Hopkins et al., 2005).
2.4.2.2 Moisture Control
For some types of subgrade, the fluctuation in moisture content is quite detrimental. In
those cases, the most effective remediation method is to control and minimize seasonal moisture
variations in the subgrade.
One of the most important aspects of a successful road design is drainage. Rollings and
Christie (2002) noticed that the lack of adequate surface drainage is one of the critical factors
leading to problems with both collapsible and expansive subgrade soils. Some obvious drainage
problem signs should be monitored such as water ponding in the drainage ditches, soft spots in
the ditch, or the presence of plants and weeds that grow best in saturated or submerged
environments. The new Mechanistic-Empirical (M-E) Design Guide (AASHTO, 2002)
38
recommended improving surface drainage by lowering the ground water level, intercepting the
lateral flow of subsurface water beneath the pavement structure, and removing the water that
infiltrates the pavement’s surface. For instance, where climate is suitable, it may be possible to
place a permeable layer over a swelling soil and limit or prevent drainage from it. Moisture
buildup in this layer maintains the soil in a stable, saturated condition. Drainage ditches, sloped
sections, water bars, cross-drains and inlet-outlet protections are recommended so that water
does not accumulate in the median.
Vegetation transpiration may significantly decrease the moisture content of active soils
and cause shrinking and deformation. Ravina (1984) and Snethen (2001) reported that climatic
extremes played a major role in causing and exacerbating damage to pavements and lightly-
loaded structures, and that large vegetation often interacts with climatic extremes to heighten the
problem. The type and location of trees should be considered in landscaping decisions,
particularly involving soil having LL > 40 and PI > 25. Based on the relative average rank
analysis, the most influential trees are Poplar, Elm, oak, and Ash. These types of trees should be
planted at least 1.5 to 3 ft beyond the anticipated mature drip line or the anticipated mature
height of the tree from pavements (Snethen, 2001). Chen and Tian (1985) suggested using a
lime trench between the structure and the tree to create a moisture transfer barrier. The depth of
the trench should be 6 ft and the lime fillings should be 4 to 8 in. The first “proximity rule” of
distance to height of tree ratio (D:H) greater than one are widely used to avoid soil shrinkage
settlement and damage to structures (Ward, 1953; Biddle, 1983 and 2001; Tucker and Poor,
1978) in New Zealand, Wesseldine (1982) indicated a threshold value of D:H of 0.75 for single
trees to cause damage and 1.0 to 1.5 for groups of these trees.
2.4.2.2 Geosynthetics
The adoption of geosynthetic for pavement aims to improve long-term bearing capacity
and performance of the road. There are eight types of geosynthetics: geotextiles, geogrids,
geonets, geomembranes, geosynthetic clay liners, geopipe, geofoam, and geocomposties
39
(Koerner, 2005). Geotextiles and geogrids are the most popular types of geosynthetics used in
the road construction industry. Geotextiles are textiles consist of synthetic fibers rather than
natural ones. These synthetic fibers have woven, non-woven, or knitted textile fabric. Geogrids
are plastics formed into a very open, grid-like configuration. Geofoams are lightweight foam
blocks that can be stacked and provide lightweight fill in numerous applications. Geocomposites
consist of a combination of geotextiles, geogrids, and/or other geosynthetics in a factory-
fabricated unit.
Geogrids have higher tensile strengths than geotextiles. Geogrids should be used on
weak subgrades with CBR values less than 3 (Tutumluer and Kwon, 2005). Several researchers
believe that the use of geogrids can effectively reduce the aggregate base thickness requirements
when compared to the unreinforced section results. Geogrids with higher tensile strength and
high aperture stability moduli have been found to give overall higher geosynthetic stiffness and
hence work better than geotextiles (Giroud and Han, 2004a, b).
The four major functions of geosynthetics used in pavements are: reinforcement,
separation, filtration and drainage (Helstrom et al. 2007). Adding a geosynthetic layer can
increase bearing capacity of a pavement structure by forcing the potential bearing capacity
surface to develop along alternate, higher shear strength surfaces. The geosynthetic
reinforcement can absorb additional shear stresses which would otherwise be applied to the
problematic subgrade. If rutting occurs, geosynthetic reinforcement is distorted and thus
tensioned. Due to its stiffness, the curved geosynthetic exerts an upward force supporting the
wheel load and thus the lateral restraint and/or membrane tension effects may also contribute to
load carrying capacity (Hufenus et al., 2006).
Geosynthetics have been used successfully for many pavement projects. Their benefits
include: extend service life, reinforce and inhibit reflection of cracks, facilitate compaction,
improve bearing capacity, reduce necessary fill thickness, diminish deformations, delay rut
formation, prevent water penetration to subgrade and reduce subgrade moisture susceptibility
(Gurung, 2003; Hufenus et al., 2006).
40
The inclusion of geosynthetics in flexible pavement design is difficult since a number of
uncertainties arise when geosynthetics is applied under distress. Based on their main targeted
function, geosynthetics can be placed below or within the overlay, within base layer, near base-
subgrade interface, or within subgrade layers. Low-volume road pavements typically consist of
a thin asphalt surface layer over an aggregate base layer. The combined surface and base layers
act together to support and distribute traffic loading to the subgrade. However, weak clayey
subgrades are often water sensitive and, when wet, may soften and deflect. Stresses developed at
the bottom of the granular layer will cause rutting and eventually, pavement cracking (Hopkins
and Sharpe, 1985; Hopkins and Beckham, 2000). To lessen, or prevent, rutting of the aggregate
layer during construction, or cracking due to base deflection after construction, geosynthetics
may be placed at, or near, the bottom of the granular base, or on top of the finished subgrade
(Figure 2.9). Use of geosynthetic reinforcement in such situation is gaining favor (Hufenus et
al., 2006; Hopkins et al., 2005)
Geosynthetics
Figure 2.9: Improving Pavement by Using Geosynthetics (from Hopkins et al., 2005).
Table 2.3 gives an example of suggested appropriate geotextile for different survivability
levels. Data are summarized by Cicoff and Sprague (1991) based on their test results of using
lightweight geotextiles as permanent road stabilization.
41
Table 2.3: Geotextile Specifications for construction Survivability in Low-Cost Low-Volume Roads (from Cicoff and Sprague, 1991)
Survivability Level Subgrade Conditions Base course Thickness* Geotextile
Mass/Area Low Dry, firm, flat > 6” compacted 4 oz/sy
Moderate Water sensitive, flat > 3”-4” compacted 6 oz/sy
High Water sensitive, grade>2% > 3”-4” compacted 8 oz/sy * For base course lifts less than 3”, required survivability should be increased one level (i.e. low to moderate).
Inclusion of geosynthetics in both wet and dry conditions increases the tensile strength of
the subsoil (Gurung, 2003; Abd El Halim, 1983). The placement of a geotextile beneath an
aggregate section increases the permissible stress on a subgrade by a factor of 1.64 to 2.0.
(Steward et al., 1977; Giroud and Noiray, 1981). Similar result is reported by Montanelli, et al.
(1999) with an increased 1.5 to 2 structural layer coefficient of geogrid reinforced flexible
pavement. The authors of the RACE design software (www.geotextile.com) recommend using
an average design improvement factor of 1.8. Kwon, et al. (2008) demonstrated the benefit of
using geogrids in pavement base course reinforcement based on a full-scale test study. Lower
subgrade vertical deformations and base course vertical and horizontal deformations were
measured in the geogrid reinforced section when compared to the deformations recorded for the
unreinforced control section. Cicoff and Sprague (1991) indicated that geosynthetics may or
may not enhance initial pavement performance, but will likely enhance future pavement
performance. However, the benefit data could not be utilized for section to section comparisons,
measured values of stress, strain and deflection are highly case specific.
2.6 CURRENT FLEXIBLE PAVEMENT DESIGN SOFTWARE AND LIMITATIONS
2.6.1 TxDOT Flexible Pavement Design System (FPS-19)
The Flexible Pavement Design System (FPS-19) is the preferred method for designing
flexible pavements in Texas. It provides a methodology for selecting a complete pavement
design strategy which includes initial construction and rehabilitation or reconstruction. The
42
material properties required by the FPS-19 to perform the pavement design are the moduli of
pavement layers. These values are backcalculated from the Falling Weight Deflectometer
(FWD) data using the MODULUS software system. Along with the modulus the expected
number of 20-yr 18-kip Equivalent Single Axle Loads (ESALs) is required by the FPS-19 to
determine the design thicknesses for the specified pavement materials and layers. Beside traffic
and material, environmental parameters are also considered by FPS-19. The output of the
software consists of one or more recommended strategies, depending upon the material layer
thicknesses the designer is willing to consider. For low volume roads, the adequacy of the
design with the FPS 19 in protecting the subgrade is verified using the Modified Texas Triaxial
design method.
2.6.2 AASHTO’s DARWin
DARWin is the software created based on the 1993 AASHTO Guide for Design of
Pavement Structures. It is a complete pavement design and analysis software for both initial
design and rehabilitation. The procedure requires the user to calculate a Structural Number (SN)
that will satisfy the performance requirements for an anticipated traffic over an expected life.
The equation for SN is shown below and is equivalent to the sum of a layer coefficient a, layer
thickness D, and drainage coefficient m for each layer. .,)( 33322211 etcmDamDaDaSNNumberStructural ++= (2.1)
One factor that makes this design software somewhat problematic is that layer
coefficients are not directly correlated to any universal system of measurement. AASHTO does
provide some guidelines for correlation to laboratory-derived resilient modulus and one design
option using the DARWin software is to input layer resilient moduli instead of layer coefficients.
Although, one of the main advantages of this software over the rest is the Life-Cycle Cost
Analysis it performs for each design alternative.
43
It is important to point out that none of the actual flexible pavement design software
described address intersections separately. The only considerations taken are based on previous
experiences from the designer and the adjustment to the accumulation of ESALs. None of the
described programs take into account the effect of stop/slow-moving vehicles in the permanent
deformation of pavement at intersections.
2.7 COST AND BENEFIT ANALYSIS
2.7.1 Cost Analysis
Cost analysis is a technique for the evaluation of multiple alternatives and identification
of the lowest cost alternative using financial principles. Three basic types of cost analysis
evaluation were described by Sewell and Marczak (1997): cost allocation, cost-effectiveness
analysis, and cost-benefit analysis. Cost allocation is the simplest of the three methods, since it
consists of setting up budgeting and accounting systems in a way that will let program managers
determine a unit cost.
Unit costs for road construction are usually estimated based on historic experience, either
by constructed costs or historical bids. To estimate the unit price by constructed cost, it is
necessary to consider the production rates, labor and equipment costs, profits and risks, taxes,
and material costs. The R.S. Means Construction Cost Guides are commercially available to
obtain approximate unit prices. To calculate unit costs by historic bid, it is necessary to average
the bids submitted by contractors over a certain period. The costs may be adjusted to the time of
construction.
Cost-effectiveness analysis assumes that a certain benefit or outcome is desired, and that
several alternative ways exist to achieve it. The basic question asked is “which of these
alternatives is the cheapest or most efficient way to get this benefit?” By definition, cost-
effectiveness analysis is comparative, while cost-benefit analysis usually considers only one
program at a time. Another important difference is that while cost-benefit analysis always
44
compares the monetary costs and benefits of a program, cost-effectiveness studies often compare
programs on the basis of some other common scale for measuring outcomes (Sewell and
Marczak, 1997).
The cost benefit analysis is intended to verify if the economic benefits of the project
compensate for the economic costs. The two important tools to demonstrate the benefit of a
project are benefit-to-cost-ratio and net rate of return. The benefit-to-cost ratio is the total
monetary value of the benefits divided by the total monetary value of the costs. The net rate of
return is just basically the total costs minus the total monetary value of the benefits. The idea
behind cost-benefit analysis is simple: if all inputs and outcomes of a proposed alternative can be
reduced to a common unit of impact (namely dollars), they can be aggregated and compared
(Sewell and Marczak, 1997).
2.7.2 Life-Cycle Cost Analysis
Life-Cycle Cost Analysis (LCCA) is defined by the Federal Highway Administration
(FHWA) as an analytical tool that provides a cost comparison between two or more competing
design alternatives that provide equivalent benefits for the project being analyzed. The typical
LCCA for pavement system includes costs for initial design and construction, operation and
maintenance, rehabilitation and salvage.
In 2002 the FHWA published a “Life-Cycle Cost Analysis Primer” which provided the
LCCA methodology for the evaluation of alternative infrastructure investment options. The first
step is to establish the alternatives that will accomplish the structural and performance objectives
of the project. The activity timing has to be determined for the initial and future activities
involving each project design alternative. All the related costs for construction and maintenance
throughout the analysis period for each alternative have to be included in the analysis, as well as
the effects of the construction and maintenance activities on users. With the predicted schedule
of activities all the costs during the analysis period are converted into present dollars by using a
45
technique known as “discounting”, and are finally all added up for each alternative. The
equations used to calculate the present value or discounting are the following:
( ) ⎟⎟
⎠
⎞⎜⎜⎝
⎛
+×=
knralueVFutureValueresentP
11
(2.2)
( )∑ ⎟⎟
⎠
⎞⎜⎜⎝
⎛
+×+=
knrValueFutureCostInitialValueresentPTotal
11
(2.3)
where:
r = real discount rate
n = number of years in the future when the cost will be incurred
The lowest of the cost summations of each alternative can be determined as the most cost-
effective alternative.
2.8 SUMMARY
The literature review presented above describes the characteristics and mechanisms of the
most common types of distresses on asphalt pavements and covered promising remediation
strategies for such problems at different levels of the structure. Such remediation strategies were
gathered from research and specifications by several organizations and state agencies throughout
the United States and worldwide. Some of the remediation strategies discussed apply directly to
flexible pavements at intersections. A collection of recommended strategies for each distress is
summarized in Figure 2.11.
The characteristics and methodology of TxDOT’s preferred flexible pavement design
software FPS-19, and AASHTO’s DARWin were described and their limitations were pointed
out. Different cost analysis methods were compared and discussed, and the Life-Cycle cost
analysis is described following the FHWA’s methodology.
The results from the maintenance and rehabilitation methods for flexible pavements
search are listed in Figure 2.10. The information is resourced from the summarized literature
review. The diagram provides a link between probable distresses, their sources and the
46
appropriate remediation. It divides the different distresses by the structural member or layer that
is failing. The different rehabilitation methods to repair flexible pavement are listed and divided
into subcategories depending on what type of distresses they might be suitable to repair.
Figure 2.10: Probable Appropriate Remediation for Different Layers
A matrix that links probable distresses and the appropriate remediation resourced from
the literature review is presented in Figure 2.11. The matrix aims to correct distresses by
proposing low cost alternatives that would perform at their best on low volume roads in an effort
to avoid common high cost alternatives. It divides the different distresses by the respective layer
that is failing and subcategorizes some of them by severity. The different methods to repair
flexible pavement are listed and separated into rehabilitations and maintenances. The figure
Asphalt
Base
Subgrade
Surface Rutting Instability Rutting Shoving Fatigue Cracking
Structural Rutting Shrinkage Cracking
Moisture Intrusion Structural Rutting Shrinkage Cracking
Stabilization Moisture Control
Microsurfacing Fog Seal Crack Seal Sand Seal Slurry Seal Ultra Thin Wearing Course Chip Seals Hot in Place Cold in Place PCC Overlay (Thick) Ultra-Thin Whitetopping Hot Mix Overlay HMA & RAS Overlay
Maintenance & Rehabilitation Methods Distresses Layers
Full Depth Reclamation Roller Compacted Concrete (Base) Stabilization Moisture Control
47
provides cases where a remediation is appropriate, likely or might be appropriate, not appropriate
and finally not a candidate to solve the identified predominant distress. A legend to identify the
suggestions is provided at the left bottom of the table.
Multiple maintenance and rehabilitation alternatives were evaluated in order to compile
the matrix taking in consideration current TxDOT methods and some additional low cost
alternatives. A thorough analysis of the suitability of each alternative to repair each of the
predominant distresses at intersections was necessary to fill every space in the matrix. Hicks et
al (2000) developed a framework for the selection of the most appropriate preventive
maintenance and rehabilitation treatments after reviewing existing practices. Some of the
recommendations made by Hicks were considered for the matrix along with recommendations
made by the Ontario Hot Mix Producers Association (OHMPA) on their ABCs of Pavement
Preservation (2004). One of the major factors missed by other agencies was on considering the
different types of rutting separately. Rutting source may be from different layers. The different
types of rutting require different types of remediation. The matrix on Figure 2.11 contains the
different types of rutting (surface, instability, and structural) by separate taking in consideration
that they all come from different sources and thereby should be approached differently.
All the recommendations are under the assumption of good design and construction
practices. The proper identification of distresses is essential to the proper selection of
alternatives. An extensive pavement analysis to recognize the type and cause of existing
distresses is encouraged before recurring to the matrix of solutions.
The following sections describe the development of an excel program for strategies
selection to improve and preserve flexible pavement at intersections, and the knowledge acquired
is applied into a case study.
48
AppropriateMay Be Appropriate Not AppropriateNot a Candidate
* No TxDOT specifications
Figure 2.11: Remediation Strategies for Common Distress Indicators.
Mic
rosu
rfac
ing
Fog
Seal
Cra
ck S
eal
Sand
Sea
l *
Slur
ry S
eal *
Ultr
a Th
in W
eari
ng
Coa
rse
Chi
p Se
als
Sur
face
Tre
atm
ent
Hot
in P
lace
R
ecyc
ling
Col
d in
Pla
ce
Rec
yclin
g
HM
A &
RA
P O
verla
y
Hot
Mix
Ove
rlay
HM
A &
Rec
ycle
d A
spha
lt Sh
ingl
es
(RA
S) O
verl
ay
PCC
Ove
rlay
(Thi
ck)
Ultr
a-Th
in
Whi
teto
ppin
g *
Full
Dep
th
Rec
lam
atio
nR
olle
r Com
pact
ed
Con
cret
e (B
ase)
Stab
iliza
tion
Moi
stut
e C
ontr
ol
< 3 / 8 in
3 / 8 - 1 in
> 1 in
Low
Moderate
High
Low
Moderate
High
Low
Moderate
HighMoisture IntrusionStructural Rutting
Maintenance RehabilitationA
spha
lt La
yer
Sub-
gr
ade
Structural Rutting
HMA Surfacing PCC
Flexible Pavement Treatment Selection Matrix
Deep RepairsB
ase
Shoving
Surface Rutting
Instability Rutting
Fatigue Cracking
Distress
Treatment
49
CHAPTER 3: RESEARCH APPROACH
3.1 TEXAS DISTRICTS SURVEYS
A questionnaire was developed and distributed to all Texas districts. The questionnaire,
which was concise to minimize the demand on the time of the TxDOT staff, was an initial step
that served the following purposes:
• To document the extent of the excessive distress at their intersections,
• To locate the districts that perceive they can benefit from the outcome of this study,
• To identify the current solutions typically used to remedy this problem,
• To document the perceived performance of their intersections after remediation, and
• To solicit projects that can be incorporated in this study.
The questionnaire is provided in Appendix A. The results to each question are documented
sequentially.
Question 1: Do your pavements experience distress at the intersections of low volume roads?
There were 17 responses to the question as summarized in Figure 3.1. Sixteen districts
stated that they experience distress at intersections of low volume roads.
Question 2: If yes, what percentage of the intersections experiences any type of distress?
The percentage of the intersections in each district that exhibit distress is listed in Figure
3.2. A limit of 25% distressed intersections was arbitrarily selected to distinguish those districts
that have more problems with their intersections. Based on that limit, San Antonio, Lubbock,
Houston and Fort Worth can benefit from the outcome of this research. Some of the remaining
districts were contacted to learn what factors contributed to their lack of distress at intersections.
50
1
16*
02468
1012141618
Yes No
Num
ber
of R
espo
nses
a) Responses
* - 16 Responses from 12 Districts
12
1
12
0
2
4
6
8
10
12
14
Distress No Distress NoResponse
Num
ber
of D
istri
cts
b) Districts
Figure 3.1: Results of Survey Responses to Districts Experiencing Distress at the Intersections of Low Volume Roads.
0% 25% 50% 75% 100%
Abilene
Atlanta
Brownwood
Bryan
Ft. Worth1
Ft. Worth2
Ft. Worth3
Houston
Lubbock1
Lubbock2
Lubbock3
Lufkin
Odessa
Paris
Pharr
San Antonio
Tyler*
Res
pons
e by
Dist
rict
Percent of Intersections
* - No distress at intersections
Figure 3.2: Percent of Intersections Experiencing Distress in the Districts.
51
Question 3: Approximately what percentages of distressed intersections experience the following distress severity? (total for the three categories should be 100%)
Low Severity (___%) Medium Severity (____%) High Severity (___%)
Figure 3.3 summarizes the level of severity of distressed intersections for each district.
As with Figure 3.2, a 25% limit of distressed intersections is highlighted as an arbitrary marker
to distinguish the level of severity perceived by the districts. For most districts at least 50% of
the distressed intersections are considered as low severity. Also, most districts perceive that
about 25% of the distressed intersection fall within medium severity.
0% 25% 50% 75% 100%
Abilene
Atlanta
Brownwood
Bryan
Ft. Worth1
Ft. Worth2
Ft. Worth3
Houston
Lubbock1
Lubbock2
Lubbock3
Lufkin
Odessa
Paris
Pharr
San Antonio
Percent of Distressed Intersections
Res
pons
e by
Dist
rict
High Severity Medium Severity Low Severity
Figure 3.3: Distribution of Distress Severity at Distressed Intersections.
52
Question 4: What distress types are common at your intersections on low volume roads?
As presented in Figure 3.4, all four types of distresses listed in the survey are equally
common at the distressed intersections. Other distresses documented were loss of aggregate,
potholes, rolling of seal coat, rub board or wash board effect, and edge break off.
0% 25% 50% 75% 100%
Rutting
Shoving
Cracking
Pushing
Other
Percent of Responses(16 Responses from 12 Districts)
Com
mon
Dist
ress
at I
nter
sect
ions
Other:-Loss of aggregate-Pot holes-Rolling of seal coat-Rub board effect- Edge break off
Figure 3.4: Type of Distress at Intersections.
Question 5-9 referred to the all five distresses listed in Question 4.
A sample of the question related to rutting is provided as an example in Figure 3.5 below.
(5) If rutting is an issue at intersections, please select: (check all that apply)
a) Probable cause:
? Inadequate structures - specify (ex. weak subgrade)_______________________________________
? Construction quality - please specify (ex. site preparation)__________________________________
? Traffic - please specify (ex volume, slow moving, channeled)_______________________________
? Environmental condition - please specify (ex. moisture, temperature)_________________________
? Inadequate drainage________________________________________________________________
? Subgrade type - please specify (ex. clayey, sandy)________________________________________
? Other___________________________________________________________________________
Figure 3.5: Question 5 from the Survey.
53
The results from Questions 5 through 9 are presented in five tables in Appendix B. These
results are summarized in Figure 3.6. The most prevalent causes for all distresses seem to be
heavy traffic and inadequate structure, followed by the environmental conditions and the
subgrade type. The other causes for each of the common distresses offered by the districts are
also indicated in the figure.
0% 25% 50% 75% 100%
Rutting
Shoving
Cracking
Pushing
Other
Com
mon
Dist
ress
at I
nter
sect
ions
Percent of Responses(16 Responses from 12 Districts)
Other Causes*
Subgrade Type
Inadequate Drainage
Environmental Condition
Traffic
Construction Quality
Inadequate Structures
*Other Causes: - Rutting : Hot mix, Utilities, - Shoving : Too much asphalt, Width of roadway and un-uniform subgrade (loam and sand not mixed properly), - Cracking: Age of roadway, - Pushing : Lack of vegatation on edge of pav., removal of 6-12 in. of pav. struc. on edge of roadway, and roadway elevation, - Other: Edge break off /Pot holes-Age of roadway, snow removal
Figure 3.6: Causes of Distress for Each Type of Distress.
Question 10: Please fill the table below regarding solutions you typically use to remedy each distress and provide typical performance life of each remedy.
The responses to this question are summarized in two parts. The first part is a summary
of the typical solutions. Appendix B provides tables that summarize the strategies selected by
each district. Rutting, shoving and pushing are remediated similarly and mainly by means of
full-depth reclamation (FDR), reconstruction, rehabilitation, and hot mix overlay (see Figure
3.7). Cracking on the other hand is handled mainly by pavement preservation. In addition, a
54
number of districts offered other means of remediation than those listed in the survey. For each
distress, these strategies are also listed in Figure 3.7.
.
0% 25% 50% 75% 100%
Rutting
Shoving
Cracking
Pushing
Other
Com
mon
Dist
ress
at I
nter
sect
ions
Percent of Responses(16 Responses from 12 Districts)
Other Strategies*
Full Depth Reclamation
Reconstruction
Rehabilitation
Preservation
Concrete Overlay
Hot Mix Blade Overlay
Other Stratigies* - Rutting : Rut fill & seal, spot base repair, blade level-up with maintainer, shaving cold mix overlay - Shoving : Spot base repair, mill & blade level-up with maintainer, shaving and cold mix overlay - Cracking : Crack seal, spot base repair, spot seal, crack pouring, fog seal, overlay, seal coat, scrub seal - Pushing : Spot base repair, mill & blade level-up with maintainer, widing, shaving and cold mix overlay, good edge vegitation - Other: Edge break off: Fog seal, chip seal, good edge vegitation, blade edge with no vegitation
Figure 3.7: Remediation Strategies for Distresses at Intersections.
Question 10 also inquires about the typical performance life of each remedy. The results
are presented in Figure 3.8. For all strategies listed the performance period is either 1-3 years or
3-10 yeas. For several of these strategies, the responses were mixed showing that some
strategies work better in some districts than others.
The results from the questionnaire present a good first step in understanding and
documenting the sources and problems at intersections. The results provide insight on several
areas where more investigation is, which were targeted in a second questionnaire and interviews
55
with district personnel. The summary of results from both the questionnaire and the interviews
will be discussed further in this document.
0% 10% 20% 30% 40% 50%
Hot Mix Blade Ovelay
Concrete Overlay
Preservation
Rehabilitation
Reconstruction
Full Depth Reclamation
Rut Fill & Seal*
Spot Base Repair*
Blade Level-Up*
Shaving and Cold Mix*
Mill then Overlay*
Rem
edia
tion
Stra
tegi
es
Percent of Responses1-3 Years 3-10 Years
*- Other Remediation Strategies Specified
a)Rutting
0% 10% 20% 30% 40%
Hot Mix Blade Ovelay
Concrete Overlay
Preservation
Rehabilitation
Reconstruction
Full Depth Reclamation
Spot Seal*
Crack Seal*
Spot Base Repair*
Fog Seal*
Cold Mix Overlay & Seal Coat*
Scrub Seal*
Rem
edia
tion
Stra
tegi
es
Percent of Responses1-3 Years 3-10 Years
*- Other Remediation Strategies Specified
b)Cracking
a) Rutting b) Cracking
0% 10% 20% 30% 40% 50%
Hot Mix Blade Ovelay
Concrete Overlay
Preservation
Rehabilitation
Reconstruction
Full Depth Reclamation
Spot Base Repair*
Good Edge Vegetation*
Mill & Overlay*
Shaving and Cold Mix*
Rem
edia
tion
Stra
tegi
es
Percent of Responses
1-3 Years 3-10 Years
*- Other Remediation Strategies Specified
c)Pushing
0% 10% 20% 30% 40% 50%
Hot Mix Blade Ovelay
Concrete Overlay
Preservation
Rehabilitation
Reconstruction
Full Depth Reclamation
Spot Base Repair*
Mill & Blade Level-Up*
Shaving and Cold Mix*
Rem
edia
tion
Stra
tegi
es
Number of Responses1-3 Years 3-10 Years
*- Other Remediation Strategies Specified
d)Shoving
c) Pushing d) Shoving
Figure 3.8: Typical Performance Period for Selected Remediation Strategies.
3.2 METHODOLOGY
Since the sources of distress at the intersections and the possible solutions are diverse, an
easy-to-use Microsoft Excel spreadsheet was created to incorporate the knowledge gained as a
preliminary guide for the selection of remediation strategies. The excel sheet contains a
systematic approach in incorporating the matrix of solutions presented in Chapter 2. This excel
56
sheet guides the user through the process of identifying the proper remediation methods for
flexible pavements at intersections and performing the life cycle cost analysis (LCCA) to obtain
the most economical alternative. The methodology used to develop this tool and a case study are
presented in this chapter. The methodology is schematically demonstrated in Figure 3.9. The
software may be used, in a rational manner, for the following purposes:
• Finding the appropriate repair alternatives for a given flexible pavement structure, the
dominant distress and traffic loading scenario.
• LCCA variables determination such as Initial Cost, Present Value, Total Present Value
and Salvage Value.
• LCCA graphs for comparison of the recommended repair alternatives.
• Yearly ESAL determination based on the average AADT (Average Annual Daily Traffic)
throughout the analysis period, the correlation for the number of 18 kip (80 kN0 single-
axle load applications per truck, and the percentage of traffic traveling per lane on each
direction.
A user interface manual for the spreadsheet is provided in Appendix C
Input Data
Remediation StrategiesTrafficStructural
Evaluations Life-Cycle Cost Analysis OutputInput
DataRemediation
StrategiesTrafficStructural
Evaluations
TrafficStructural
Evaluations Life-Cycle Cost Analysis Output
Figure 3.9: Methodology Diagram.
3.2.1 Input Data
The purpose of this section is to collect most of the information from users at the beginning
of the program. This information is used throughout the analysis process.
Beside the general project information, the input data required for the analysis are:
• size of the project,
• intersection traffic count and factor,
• problematic layer, predominant distress and severity, and
57
• preferred future maintenance method when rehabilitation is recommended
• analysis period and discount rate
Other information related to parameters associated with different remediations such as
unit costs and expected life has been included in Excel as default values. The default values are
used with the flexibility of modifying this information is given to the users to fit their own
conditions.
3.2.2 Evaluation
3.2.2.1 Structural Evaluation
The main purpose of this section is to evaluate the existing structural conditions of the
intersection based on the information collected. In the excel sheet, the structural evaluation is
based on visual inspection, making the visual identification of predominant distresses essential
for the analysis. The most common flexible pavement distresses at intersections are presented in
Chapter 2. Additional analysis is necessary to ensure the structural adequacy of the pavement
structure and corroborate the conclusions made by visual inspection. Field tests such as
Dynamic Cone Penetrometer (DCP) and Falling Weight Deflectometer (FWD) are good options
to determine the existing modulus of the pavement layers for rehabilitation purposes. This
information is not currently included in the preliminary guideline. However, an option will be
provided in the final product to include input from field data such as FWD and DCP.
The sources of most typical distresses at intersections can be pointed to a specific
pavement layer, thereby it is possible to identify the failing layer by recognizing the type of
distress present. For example shoving, fatigue cracking, surface rutting and instability rutting are
strictly related to failure due to the asphalt layer mixture. The source of structural rutting can be
identified by paying attention in the details of the deformation. A small hump in the middle of
the two wheel paths and narrower wheel paths indicate base deformation, while wider wheel
paths with no hump between the wheel paths indicate deformation of the subgrade layer (Fang,
58
2001). Based on the importance of the project, these behaviors could be corroborated with
further lab or field testing. The list of distresses currently incorporated into the guideline is:
• Instability Rutting
• Surface Rutting
• Shoving
• Fatigue Cracking
• Structural Rutting
• Moisture Intrusion
Identifying the magnitude or severity of the distress is also important. Severities of distresses
are usually categorized as high, moderate, and low. The distresses categorized by severity are
rutting (structural, instability, and surface) and fatigue (alligator) cracking. The remaining
distresses are not categorized and are only evaluated based on their presence. Based on the
predominant distress and the level of severity (if required), a number of remediation strategies
are proposed. However, the traffic data and other information are also used to narrow the
choices of remediation.
3.2.2.2 Traffic Evaluation
The traffic classification utilized is based on TxDOT criteria for low volume roads of less
than 500,000 cumulative ESALs for a design period of 20 years. A value of 25,000 ESALs per
year is used by the spreadsheet to classify low volume roads. Lower cost remediation
alternatives are considered in the evaluation if the traffic volume is less than this value.
Otherwise, the intersection is considered as a high-volume intersection, and the recommended
alternatives will be those typical for high volume roads, such as Portland Cement Concrete
(PCC) Overlay, Full Depth Reclamation, and Roller Compacted Concrete.
The following traffic information should be requested from the Transportation Planning
and Programming Division:
• Truck Factor,
59
• Truck Percentage
• Lane Distribution Factor
• Average Annual Daily Traffic (AADT) for the year of construction, and
• Predicted Average Annual Daily Traffic (AADT) for the end of the analysis period.
One of the considerations that should be taken at this point is the summation of the
AADTs from both roads intersecting to be able to quantify the actual number of vehicles passing
through the intersection itself. The combination of trucks as percentage of AADT is necessary to
calculate the number of heavy vehicles that will be using the road and it can be find in Table 3.1
by identifying the predominant truck classes and the type of the roads. The Truck Factor is the
correlation for the number of 18-kip single-axle load application per truck and it can be found in
Table 3.2. Finally the Lane Distribution Factor represents the percentage of truck traffic that is
traveling in the design lane and can be obtained from Table 3.3. These values introduced in
Equation 3.1 to calculate the Daily ESALs over the intersection necessary for the classification.
( )( )( )( )( )3655.02
LTTAADTAADT
ESALDaily ffi
⎟⎟⎠
⎞⎜⎜⎝
⎛ += (3.1)
where:
AADTi = Average Annual Daily Traffic during construction year
AADTf = Average Annual Daily Traffic projected at the end of analysis period
T = Truck Percentage
Tf = Truck Factor
L = Lane Distribution Factor
3.2.3 Remediation Strategies
Different distresses correspond to different solutions. A matrix that relates the most
common distresses at intersections with the common remediation methods is presented in Figure
2.11. Remediation strategies are categorized into two types; rehabilitation and maintenance,
while the distresses are categorized by layer, and then subcategorized by severities. The data in
60
the matrix is synthesized based on the literature and several expert opinions around Texas. This
data will be incorporated into the remediation tool in the second phase of research. It could also
be modified by including other distresses and or remediation strategies.
As soon as the problem is identified, the excel sheet looks up the feasible alternatives to
repair the problem from the matrix and lists them. The alternatives are differentiated in the list
by color, highlighting the “appropriate” in green and the “less appropriate” in yellow. A
description of each remediation method consider by the matrix as an alternative for the typical
distresses at intersections is contained in Appendix D.
61
Table 3.1: Distribution of Trucks on Different Classes of Highways in the United States after AI (1991)
* Including full-trailer combinations in some states + Compiled from data supplied by the Highway Statistics Division, U.S. Federal Highway Administration
Percent Trucks Rural Systems Urban Systems
Collectors Truck Class Interstate Other
Principal Minor Arterial Major
Minor Range Interstate Other Freeways
Other Principal
Minor Arterial Collectors Range
Single-unit Trucks
2-axle, 4 tire 43 60 71 73 80 43-80 52 66 67 84 86 52-86
2-axle, 6 tire 8 10 11 10 10 8-11 12 12 15 9 11 9-15
3-axle or more 2 3 4 4 2 2-4 2 4 3 2 <1 <1-4
All single units 53 73 86 87 92 53-92 66 82 85 95 97 66-97
Multiple-unit Trucks
4-axle or less 5 3 3 2 2 2-5 5 5 3 2 1 1-5
5-axle* 41 23 11 10 6 6-41 28 13 12 3 2 2-28
6-axle or more* 1 1 <1 1 <1 <1-1 1 <1 <1 <1 <1 <1-1
All multiple units 47 27 14 13 8 8-47 34 18 15 5 3 3-34
All Trucks 100 100 100 100 100 100 100 100 100 100
62
Table 3.2: Distribution of Truck Factors for Different Classes of Highways and Vehicles in the United States after AI (1991)
Truck Factors Rural Systems Urban Systems
Collectors Truck Class Interstate Other
Principal Minor Arterial Major
Minor Range Interstate Other Freeways
Other Principal
Minor Arterial Collectors Range
Single-unit Trucks
2-axle, 4 tire 0.003 0.003 0.003 0.017 0.003 .003-.017 0.002 0.015 0.002 0.006 - 0.006-0.015
2-axle, 6 tire 0.21 0.25 0.28 0.41 0.19 0.19-0.41 0.17 0.13 0.24 0.23 0.13 0.13-0.24
3-axle or more 0.61 0.86 1.06 1.26 0.45 0.45-1.26 0.61 0.74 1.02 0.76 0.72 0.61-1.02
All single units 0.06 0.08 0.08 0.12 0.03 0.03-0.12 0.05 0.06 0.09 0.04 0.16 0.04-0.16
Tractor semitrailers 0.92 0.62 0.37 0.91 0.37-0.91 0.98 0.48 0.71 0.46 0.4 0.40-0.98
4-axle or less 0.62 1.25 1.05 1.67 1.11 1.05-1.67 1.07 1.17 0.97 0.77 0.63 0.63-1.17
5-axle* 1.09 1.54 1.04 2.21 1.35 1.04-2.21 1.05 1.19 0.9 0.64 - 0.64-1.19
6-axle or more* 1.23 1.21 0.97 1.52 1.08 0.97-1.52 1.05 0.96 0.91 0.67 0.53 0.53-1.05
All multiple units 1.04 0.38 0.21 0.3 0.12 0.12-0.52 0.39 0.23 0.21 0.07 0.24 0.07-0.39
All Trucks 0.52
* Including full-trailer combinations in some states + Compiled from data supplied by the Highway Statistics Division, U.S. Federal Highway Administration
63
Table 3.3: Lane Distribution Factor after AASHTO (1986)
No. of Lanes in Each Direction
Percentage of 18-kip ESAL in Design Lane
1 100 2 80-100 3 60-80 4 50-75
3.2.4 Life-Cycle Cost Analysis
LCCA is used to quantify the total economic value of a project over its life. The main
purpose of LCCA is to evaluate the long-term repercussions of initial pavement design on the
future cost of maintenance necessary to maintain an acceptable service level for a specified time.
The parameters used for the LCCA include initial costs, future maintenance costs over the life of
the project, and salvage value at the end of the analysis period. Since this research is focused on
rural road intersections with low daily traffic, the user costs (user delay costs, vehicle operating
costs, and crash costs) and the construction activity timing were omitted from the analysis.
The analysis period is essential for the LCCA. To compare the recommended
alternatives economically, it is necessary that all alternatives are under the same analysis period.
Unit costs and expected lives of each alternative were collected from the literature and provided
in the program as default values for the analysis. These costs are expected to vary with location
and the expected lives would also vary depending on the environmental conditions. Thus, these
values can be readily adjusted by the user during the analysis. A table with the default unit costs
for each alternative is also provided. At this point, the user can modify the costs according to
their experience and location. For all the rehabilitation alternatives the option of selecting a
maintenance method to be performed within the life of the rehabilitation is provided. TxDOT
(2006) recommends that the selected rehabilitation design strategy for flexible pavements should
provide a minimum initial performance period of 8 years before an overlay is required.
Therefore, the first maintenance is recommended to be performed 8 years after completing the
64
rehabilitation. The expected life of the maintenance method selected is used to determine the
timing between maintenances during the analysis period.
The cost of each alternative is easily calculated with the total area to be repaired by the
unit cost of construction and materials provided. While the initial cost remains the same, all the
future costs (including salvage value) are adjusted to present value with Equation 3.2 by using
the discount factor provided by the user and the accumulated time from the beginning of
analysis. Salvage value is calculated as the remaining value of the last maintenance when it still
has a remaining life over the analysis period. Salvage is also adjusted to present value and is
subtracted from the cost summation. The equations used to calculate the present value or
discounting are the following:
( ) ⎟⎟⎠
⎞⎜⎜⎝
⎛
+×=
knralueVFutureValueresentP
11
(3.2)
( )∑ ⎟⎟⎠
⎞⎜⎜⎝
⎛
+×+=
knrValueFutureCostInitialValueresentPTotal
11
(3.3)
where:
r = discount rate
n = number of years in the future when the cost will be incurred
3.2.5 Output
The results from all the alternatives based on LCCA are listed and rank ordered from the
most economical to the most expensive. The color differentiation is still present at this point to
distinguish between “recommended” and “less appropriate” alternatives. The final table displays
the total present value, initial cost, salvage value and cost of routine maintenances for each
alternative. The option of ranking the alternatives by the lowest initial cost or the lowest total
present values cost is given to the user. The excel sheet provides enough cost information to
allow the user to make decisions based on their own criteria. It is important to mention that the
alternatives highlighted in green are recommended.
65
CHAPTER 4: CASE STUDY: INTERSECTION OF SH 155 AND SH 49 FORENSIC EVALUATION
4.1 BACKGROUND
The intersection of SH 49 and SH 155 is located in the Atlanta District. Figure 4.1
depicts the areal view of the intersection. This is a typical rural intersection with a 4-way light
signalization consisting of flexible pavement only. The typical cross section is presented in
Figure 4.2. The SH 155 pavement section consisted of a 2.0 in. AC over 11 in. of base, with the
upper 8 in. lime treated. The SH 49 pavement section consisted of a 4.0 AC layer over 12 in. of
lime treated base over subgrade. A soil report of the intersection and surroundings was obtained
from the Natural Resources Conservation Service (NRCS) website. The predominant type of
soil in the area is classified as Bowie fine sandy loam. This intersection was identified by district
personnel of potential location due to the severity of distresses around the intersection area. The
blue prints of these sections were provided by the district office.
SH155
SH49
SH155
SH49
Figure 4.1: Aerial View of SH 155 and SH 49 Intersection.
66
a) SH 155 Pavement
b) SH 49 Pavement
Figure 4.2: Cross-sectional Pavement Design for SH 155 and SH 49
4.2 CONDITION SURVEY
The investigation concentrated on the intersection portion of the roadway. With the
assistance from the District personnel, 500 ft sections of the road on either side of the
intersections were closed off to traffic. A thorough inspection was carried out on all legs of the
intersection. The primary distress observed were rutting of the surface layer. The intersection, at
the southbound approach on SH 155 was rutting. No humps could be seen on the sides of the
ruts, so it can be assumed that it might not be a mix problem, but maybe structural rutting.
Figure 4.4 shows different views of the intersections along SH 155 with visible distresses. Loss
of aggregate was evident on the rutted areas as well as some bleeding and flushing between
wheel paths.
67
Figure 4.3: Geometry Design of SH 155 and SH 49 Intersection
Figure 4.4: Views of the Conditions of SH 155 and SH 49 Intersection.
As shown in Figure 4.5, the maximum rut depth was 0.5 in. on SH 155. This distress can
be classified as Moderate Severity Structural Rutting. Another typical intersection distress
observed was fatigue cracking with low to high levels of severity, increasing in severity as one
approached the intersection. Other distresses included transversal and block cracking specially
after crossing the intersection.
68
Figure 4.5: Rut Depth Measurement on SH 155.
The SH 49 inspection started 500 ft west of the intersection and extended 500 ft east of
the intersection. The first 300 ft consisted of a different asphalt mix than the mix closer to the
intersection. On the west side, close to the intersection on the eastbound SH 49, a section of
approximately 42 yards in length had been milled so no rut profile could be taken at this point.
Based on the cores, several lifts were added with time to this intersection. Cores were not
extracted from the milled section. It is suspected that the section was heavily rutted and the
maintenance crew had overlaid that portion. In addition, transversal cracking could be seen all
the way along the 500 ft approach while severe block cracking was seen at the intersection. In
some area, the severe block cracking contributed to generation of secondary distresses as
depicted in Figure 4.6.
Figure 4.6: Cracking Resulting in Potholes on SH49.
69
4.2 DATA COLLECTION
For coring purposes, four strategic locations were selected, 2 locations per road, with one
location 500 ft away from the intersection, and the other location within 100 ft away from the
intersection, all in the approaching lanes. Three cores were extracted from each location, one
per wheel-path and one in the middle of the wheel-paths, making it a total of 12 core extractions
as marked in Figure 4.7.
Figure 4.7: Location of the Core Extractions.
Deflection data was collected using a Falling Weight Deflectometer (FWD). Both roads
intersecting were evaluated using this method. Fwd data along SH 155 were collected 500 ft
north of the intersection to 500 ft past the intersection. Data was collected at 25 ft intervals
except in the vicinity of the intersection where data was collected more densely (see Figure
4.8a). The same was performed for SH 49, starting 500 ft west of the intersection (see Figure
4.8b). An air-launched Ground Penetrating Radar (GPR) was also used along these two roads.
1
4 2
3
1
4 2
3
SH155
SH49
N
70
a) SH155 b) SH49
Figure 4.8: FWD Collection on SH155 and SH49 Images
4.3 DATA ANALYSIS
4.3.1 Core Analysis
Figure 4.9 shows the coring process and a sample of the cores that were extracted.
Dimensions and weight of every core were measured, and the V-meter test was performed on
each sample to calculate the modulus of the asphalt layer from different locations. The asphalt
content of each core was determined using an ignition oven. Sieve analysis was carried out on
Figure 4.9: Coring Process Images.
71
the retrieved aggregates from the oven to determine the gradation. Summaries of the analysis
results and images of each core extracted are included in Appendix E.
The average thickness of each set of cores is plotted in relation with the distance from the
intersection in Figure 4.10. The error bar indicates low variability in the thickness of 3 set of
cores, except for the first set of cores extracted 500 ft north from the intersection on SH 155. A
decrease in thickness as approaching the intersection is evident along SH 49, while on SH 155
the asphalt layer thickness seems to remain constant. The surface layers of the two sets of cores
from SH 49 were different. Severe stripping was observed in the cores away from the
intersection along SH 155 that might have prompted maintenance.
0
1
2
3
4
5
500 100 75 500
Distance from Intersection, ft
Thic
knes
s, in
SH 155 SH 49
Intersection
Figure 4.11: Core Average Thicknesses as Approaching the Intersection.
Figure 4.12 illustrate the decrease in air voids as approaching the intersection, which
might be a result of the over densification of the surface layer produced by the slow moving
loads while approaching the intersection. The high values of air voids 500 ft away from the
intersection on SH 155 are because of the stripping of the materials.
72
0%1%2%3%4%5%6%7%8%9%
10%11%
500 100 75 500
Distance from Intersection, ft
Air
Void
s
SH 155 SH 49
Intersection
Figure 4.12: Core Average Air Voids as Approaching the Intersection.
The modulus trends as approaching the intersection are the opposite of the air voids for
both roads as seen on Figure 4.13. The modulus was measured on every core using the V-meter,
since the SH155 outer wheel path core at 500 ft away was damaged it affected the modulus
readings from the V-meter and thereby the trend.
0
100
200
300
400
500
600
700
500 100 75 500
Distance from Intersection, ft
Mod
ulus
, ksi
SH 155 SH 49
Intersection
Figure 4.13: Core Average Design Modulus as Approaching the Intersection.
73
The variations in the asphalt contents of the cores are shown in Figure 4.14. Higher
asphalt content close to the intersection may be a sign of aggregate loss caused either by
aggregate segregation, and/or the high stresses under the breaking and turning of vehicles.
0%1%2%3%4%5%6%7%8%9%
10%
500 100 75 500
Distance from Intersection, ft
Asp
halt
Con
tent
SH 155 SH 49
Intersection
Figure 4.14: Core Asphalt Contents.
In order to verify the lime stabilization of the bases, Phenolphthalein was used. The
reaction occurred just on the second and third sets of cores as seen on Figure 4.15, but no
reaction occurred on the first or fourth set of cores. A complete base core could only be
extracted from the third location. Higher lime content was perceived for the third location.
a) Set 2 on SH 155 b) Set 3 on SH 49 c) Set 4 on SH 49
Figure 4.15: Phenolphthalein Test for Lime on Base Material
74
4.3.2 FWD Analysis
Figure 4.16 illustrates the deflection results obtained from the FWD along the SH 155
section. Deflection values from the first two sensors are greater close to the approach of the
intersection, indicating lower stiffness of this section of the road. After passing the intersection
deflection values decreased dramatically and remained fairly constant. The third and fourth
sensors also detected a slight increase in deflection for a 150 ft section before the intersection,
providing a clue that the source of the problem might come from the base layer. Last 3 sensors
did not detect a significant deflection, thereby can be assumed that the source of the problem
does not go deeper than the base layer.
0
5
10
15
20
25
30
-500 -400 -300 -200 -100 0 100 200 300 400 500
Distance, ft
Def
lect
ion,
mils
Sensor 1 Sensor 2 Sensor 3 Sensor 4 Sensor 5 Sensor 6 Sensor 7
Intersection
Figure 4.16: FWD Deflection Results on Southbound SH 155.
Figure 4.17 illustrates the deflections obtained from the SH 49 section. The first 200 ft
with the different mix have a considerable lower deflection than the rest of the road. The
increment in deflection after the first 200 ft remains constant until reaching the intersection,
where a decrease in deflection is perceived. After passing the intersection the deflections
75
increase again to a constant value for the next 250 ft, only a high point is seen 400 ft after the
intersection. The structure is more susceptible to deflection along the 300 ft section before
reaching the intersection. The third and fourth sensors also detected an increase in deflection as
approaching the intersection and slight variations in deflection through the last 200 ft before the
intersection. The higher deflection levels detected by the third and fourth sensors as approaching
the intersection are consistent with the lack of stabilization on the fourth coring location (100 ft
before the intersection). Although the soil tested from core location 4 (100 ft from intersection)
did not showed evidence of lime, contrary to location 3 (500 ft from intersection), no permanent
deformation could be seen at this place. The last three sensors did not detect a significant
deflection; thereby one can assume that the source of the problem might be no deeper than the
base.
0
5
10
15
20
25
30
-500 -400 -300 -200 -100 0 100 200 300 400 500Distance, ft
Def
lect
ion,
mils
Sensor 1 Sensor 2 Sensor 3 Sensor 4 Sensor 5 Sensor 6 Sensor 7
Intersection
Figure 4.17: FWD Deflection Results on Eastbound SH 49.
76
4.3.3 GPR Analysis
The PAVECHECK software (Liu and Scullion, 2008), developed to merge the FWD and
GPR data together with digital video images of surface condition was used Figure 4.18 is a
sample of the data collected on SH 155 and SH 49 as approaching the intersection.
Figure 4.18- Sample of the GPR Data Close to the Intersection of FM155 and FM49.
Figure 4.19 contains the GPR, FWD and Core thickness data all together for comparison
analysis of SH 155. GPR plot is in terms of thickness of the upper layer, while the FWD data
corresponds to the deflection readings of the first sensor. The core thicknesses compared well
with the GPR thicknesses. GPR thickness readings are reasonably constant until approximately
30 ft before SH 49 center line, where the thickness increases to over 4 in. and then decreases to 1
FM155
FM 49
77
in. after crossing SH 49 and slowly increasing its way back to a little over 2 in. along the
acceleration section.. The constant GPR measured thickness before and after the intersection
may be an indicator that the asphalt layer may not be the source of rutting.
0
1
2
3
4
5
6
-500 -300 -100 100 300 500
Distance, ft
Thi
ckne
ss, i
n.
0
5
10
15
20
25
30
Del
fect
ion,
mils
GPR Core OWP Core Center Core IWP FWD
Intersection
Figure 4.19: GPR, FWD and Cores on SH 155.
Similar results for SH 49 are illustrated in Figure 4.20. As mentioned before, the first
300 ft of the survey consisted of a different asphalt mix. The HMA thickness is about 3.5 in. to 4
in. before the intersection, increasing to around 5.0 in. past the intersection. The HMA layer
thickness at the intersection seems to be controlled by the design of SH 49 but with an additional
0.5 in. slurry seal.
A relationship between thickness and deflection is appreciable. The first half section of
SH 49 which is thinner provides higher deflections, while past the intersection that trend
reverses. No rutting appeared on the first half of the road, most likely the severe block cracking
is the reason for the high deflection values.
78
0
1
2
3
4
5
6
-500 -300 -100 100 300 500
Distance, ft
Thi
ckne
ss, i
n.
0
5
10
15
20
25
30
Del
fect
ion,
mils
GPR Core OWP Core Center Core IWP FWD
Intersection
Figure 4.19: GPR, FWD and Cores on SH 49.
4.4 CONCLUSIONS
The evidence from the visual condition survey on SH 155 suggests that the absence of
humps on the sides of the ruts indicates that the source of rutting is not the asphalt layer, but an
underneath layer. The GPR results corroborate the same assumption by showing a consistency
in the thickness of the asphalt layer. Deflection readings from FWD suggest that the problem
does not come from a layer deeper than the Base. Although some shoving and other asphalt mix
related distresses existed, the predominant and “deeper” distress for SH 155 was classified as
Base Moderate Structural Rutting.
High Severity Block Cracking was the most visible distress on SH 49. Aging of the
asphalt or wrong binder selection could be the causes of the failure. No significant permanent
deformation could be perceived on the approach, indicating that the base layer is still in good
condition. Also GPR results showed thickness uniformity for the asphalt layer. Severe block
cracking might be the source of the high deflection levels detected by FWD.
79
The intersection itself showed low levels of deflection, indicating that the base at this
point is still in good condition. But still, the asphalt layer suffered from cracking, raveling and
deformation.
80
CHAPTER 5: EXCEL SPREADSHEET ANALYSIS OF SH 155 AND SH 49 INTERSECTION
To demonstrate the utility of the Excel spreadsheet, the Atlanta District site described in
the previous chapter is evaluated for the selection of a remediation strategy. The intersection is
evaluated based on the field and laboratory studies carried out to identify the source of the
problem. As soon as the source of the problem is identified, the spreadsheet can assist in
selecting a list of alternatives that are suitable to repair the existing pavement. Based on an
LCCA of all alternatives in the worksheet, the user can select the most cost-effective option or
the one that fits best to the District’s normal practices.
The spreadsheet consists of the following 6 sections
1. General Project Information
2. Analysis Options
3. Traffic Conditions
4. Evaluate Existing Pavement Condition
5. Repair Alternatives
6. Life Cycle Cost Analysis
The excel spreadsheet focuses on finding solutions for the specific source of the problem,
in this case Base Moderate Structural Rutting. The area that suffers from this predominant
distress should be calculated as an input parameter for the spreadsheet.
5.1 SECTION 1: GENERAL PROJECT INFORMATION
This section is intended for the documentation of the site. Figure 5.1 illustrates the initial
input setup. The project name, district, county and roads intersecting need to be input, as well as
the control, section and job numbers, if available. In this case the name of the project is
“Intersection Repair” of “SH49 and SH155” in “Cass” County, in “Atlanta” District.
81
Figure 5.1: Section No. 1 with General Project Information Input.
5.2 SECTION 2: ANALYSIS OPTIONS
The information provided in this section is used to calculate the costs and allow
performing the LCCA. Figure 5.2 illustrates the required input. The first item on the list is the
“Area to be Repaired,” which has to be input in square yards. This item is essential to calculate
the Initial Cost that will be later used for obtaining the Present Value, and the Salvage and Total
Present Values. Figure 5.3 shows the area selected to be repaired. An approximate area of 6,400
yd2 was calculated for all the lanes that need to be repaired.
Figure 5.2: Section No. 2 with Information about LCCA Analysis Options.
82
Figure 5.3: Schematic of the Recommended Area for Repair on SH 155.
The “Beginning of Analysis Period” is the year in which the construction is planned to
start. The Analysis Period is used to compare the recommended alternatives under the same
period by adding all the rehabilitation and maintenance costs required within that period for each
alternative, and subtracting the Salvage Value if any. For this case a period of 30 years was
selected to perform the analysis and comparison of the alternatives. Moreover, the Analysis
Period is also used to compute the factor that brings the future costs to present worth. Likewise,
the Discount Rate is utilized a (Equation 3.2) for finding the Present Value of the amount to be
spent in the future, and it is usually around 4%.
5.3 SECTION 3: TRAFFIC CONDITIONS
The information obtained from this section is used to classify the traffic volume of the
intersection. Although the traffic counts for this site were not collected it was indeed known to
be a low volume intersection. The AADT values at this point were assumed to proceed with the
evaluation as shown in Figure 5.4. A truck Percentage of 50 was selected assuming that both
single and multiple unit trucks traffic the intersections. A truck factor of 0.52 was selected from
Table 3.2 following the assumption that all classes of trucks will be traveling the intersection. A
conservative lane distribution factor of 1.0 was chosen. By utilizing these assumptions the
Yearly ESALs were kept below the limit of 25,000 for low volume roads.
500ft 500ft
SH155 SH49
500ft 500ft
SH155
500ft 500ft
SH155 SH49
83
Figure 5.4: Traffic Conditions Input Parameters.
5.4 SECTION 4: EVALUATE EXISTING PAVEMENT CONDITION
The results from the site investigation are introduced in the program at this time,
including the layer identified as the source of the problem, and selecting the predominant distress
and its severity. The layer selection options are “Asphalt”, “Base”, and “Subgrade”, while the
distress selection options are those described in Section 3.2.2.1. Finally for this section the
severity of the distress is to be selected among “Low”, “Moderate”, “High”, or “No Severity”.
The last severity option is only for those distresses which are not subcategorized by severity.
Figure 5.5 illustrates the 3 selection boxes filled with the predominant distress. Base
structural rutting of moderate severity was the identified predominant distress at the intersection.
While the same distress was continuous along the 1000 ft section (both directions) of SH 155,
SH 49 suffered mostly of cracking for the rest of the analyzed section. However, as structural
rutting was the most severe problem, the selection process should first aim to correct it.
Figure 5.5: Section No. 4 for the Evaluation of the Existing Pavement.
84
5.5 SECTION 5: REPAIR ALTERNATIVES
The purpose of this section is to present all the possible repair alternatives extracted from
the matrix of solutions from Chapter 2 based on the identified predominant distress provided by
the users in Section 4. This section contains two tables. The first table (Figure 5.6a) presents all
the possible maintenance and rehabilitation alternatives for the problem obtained from the matrix
of solutions. The “Recommended” and “May be Appropriate” alternatives are differentiated by
highlighting the first ones in green and the second ones in yellow (a color legend is provided).
The same table provides default values for materials and construction costs, and life expectancies
for each alternative, which can be adjusted by the user, based on her/his experience or
knowledge. These default values, which were collected form the literature and are provided in
the “Cost & Life” sheet.
The second table illustrated on Figure 5.6b list the rehabilitation alternatives separated
from the maintenance alternatives, and allows the user to select from a box list of maintenance
method to be performed within the life of each of the rehabilitation alternatives throughout the
analysis period. The maintenance alternatives are the same as those in the matrix of solutions.
This table also provides default values for materials and construction costs, and life expectancies
of each maintenance alternative selected, also allowing the user to modify them. For the sake of
comparing all the alternatives under the same conditions microsurfacing was selected for all
alternatives in this example.
85
a) All Alternative Costs and Life Expectancies
b) Maintenance Method Selection for Rehabilitation Alternatives.
Figure 5.6: Section 5 Tables for Costs and Life Expectancies.
5.6 SECTION 6: LIFE CYCLE COST ANALYSIS
The life cycle cost analysis of all the alternatives takes place in this section. The costs of
all alternatives are compared under the same analysis period. The option of ranking the
alternatives by “Initial Cost” or “Total Present Value” is given through a selection box. As seen
on Figure 5.7, the alternatives maintain the color label to differentiate between the recommended
and may be appropriate alternatives. Full Depth Reclamation (FDR) with or without
stabilization are the most appropriate alternatives based on performance. The performance is
uncertain for the rest of the alternatives in the list. HMA and RAP Overlay is the most
economical alternative, although it is not fully recommended, as highlighted in yellow. At this
point the district personnel experience takes and important role in the decision making.
86
Figure 5.7: Section No. 6 with Ranked Cost Results.
The present value costs of the alternatives are compared in a graph created by the
spreadsheet as seen on Figure 5.8. The values for each alternative are equivalent to the
summation of present value costs of all the activities within the same analysis period. This graph
allows the user to visually compare the alternatives and identify the most economical alternative
over the analysis period.
Figure 5.8: All Alternative Present Value Comparison Graph.
87
Figure 5.9 is a chronological plot of the costs that are expected to be incurred on the
intersection for the length of the analysis period for the most economical alternative, in this case
HMA and RAP Overlay and its respective microsurfacing maintenance selected in Section 5.
The green bars represent rehabilitation and maintenance costs while the red bar represents the
salvage value at the end of the analysis period. The tallest bars indicate the rehabilitation
expense which occur every 15 years, the life expectancy of HMA and RAP Overlay. The short
green bars are the microsurfacing expenses done within the life of the rehabilitation.
The graph on Figure 5.10 is similar to the previous graph, but gives the users the option
of selecting any of the other alternatives from a box list to visually compare it with the most
economical one. Full Depth Reclamation is selected to be compared with the most economical,
since it is has the lowest cost from the two recommended alternatives. At a total present value of
$120,000 for a period of 30 years, Full-Depth Reclamation is recommended as it is the most
economical of the most appropriate alternatives.
Figure 5.9: LCCA Plot for the Most Economical Alternative.
88
Figure 5.10: LCCA Plot for Full Depth Reclamation.
The analysis just performed was focused in resolving the base structural problem on SH
155 only. For the rest of the intersection, on SH 49, an overlay is recommended. The analysis
on SH 49 provided clues suggesting that the problem was either bad construction practices or
design. The base at this section is still in good conditions, and should be left as is. It is
recommended that the asphalt layer be completely removed and replaced.
89
CHAPTER 6: SUMMARY AND CONCLUSIONS
6.1 SUMMARY
The literature review describes the characteristics and mechanisms of the most common
types of distresses of asphalt pavements and covered promising remediation strategies for such
problems at different layers of the structure. Such remediation strategies were gathered from
research and specifications by several organizations and state agencies throughout the United
States and worldwide. The characteristics and methodology of TxDOT’s preferred flexible
pavement design software FPS-19, and AASHTO’s DARWin were described and their
limitations were pointed out. Different cost analysis methods were compared and discussed, and
the Life-Cycle cost analysis as per the FHWA methodology is described.
A matrix that links probable distresses and the appropriate remediation resourced from
the literature review was created. The matrix aims to correct distresses by proposing low cost
alternatives that would perform at their best on low volume roads in an effort to avoid common
high cost alternatives. The matrix provides cases where certain remediation is appropriate, likely
or might be appropriate, not appropriate and finally not a candidate to solve the identified
predominant distress.
One of the major treatment selection factors missed by pavement agencies was on
considering the different types of rutting separately. Rutting source may be from different
layers. The different types of rutting require different types of remediation. The matrix created
contains the different types of rutting (surface, instability, and structural) taking into
consideration that they come from different sources and thereby should be remedied differently.
A questionnaire was developed and distributed to all Texas districts. The questionnaire
served the following purpose:
• To document the extent of the excessive distress at their intersections,
• To locate the districts that perceive they can benefit from the outcome of this study,
• To identify the current solutions typically used to remedy this problem,
90
• To document the perceived performance of their intersections after remediation, and
• To solicit projects that can be incorporated in this study.
An easy-to-use Microsoft Excel spreadsheet was created to incorporate the knowledge gained as
a preliminary guide for the selection of remediation strategies. The excel sheet represents a
systematic implementation of the matrix of solutions, which is intended to guide users
throughout the process of identifying the proper remediation methods for flexible pavements at
intersections and to perform the Life Cycle Cost Analysis (LCCA) to obtain the most economical
alternative.
A thorough study of the intersection between SH 155 and SH 49 was performed. Visual,
destructive and non-destructive analyses were performed to assess the condition of the pavement
at the intersection. The evidence from the visual condition survey on SH 155 suggests that the
base layer was the source of rutting. The GPR results corroborated the same assumption by
showing a consistency in the thickness of the asphalt layer. Deflection readings from FWD
suggested that the problem did not come from a layer deeper than the base. The predominant
distress for SH 155 was classified as Moderate Structural Rutting of the base. High severity
block cracking was the most visible distress on SH 49. Aging of the asphalt or wrong binder
selection could have been the causes of the failure with base being in good condition. Severe
block cracking might have been the source of the high deflection readings by FWD.
Finally, as a preliminary utilization of the Excel spreadsheet at the intersection of SH 155
and SH 49 was evaluated after having identified the source of the problem for the selection of a
remediation strategy. The spreadsheet performed LCCA for a list of alternatives extracted from
the matrix of solutions for the users to compare. At a Total Present Value of $120,000 for a
period of 30 years, Full-Depth Reclamation is recommended as it is the most economical of the
trustable alternatives.
91
6.2 RECOMMENDATIONS AND FUTURE WORK
Five sites have been visited so far and the results from each site are being documented.
Knowledge gained from these sites will be used in the development of the final guideline. Based
on the experience gained during our visits to the first set of sites, a checklist that details the
information that should be collected and gathered for a more comprehensive analysis is
presented in Appendix F. This list will serve as a guide for future sites. The list covers data such
as traffic, geometry, condition survey, field testing such as FWD and coring, and laboratory
testing.
The project will continue developing a final guideline. The information will be
incorporated in a concise but attractive document that can be used as a guidebook by TxDOT
personnel. An electronic version of the guide will also be provided with appropriate hyperlinks
to definitions, relevant TxDOT specifications, step-by-step procedures and other web-pages that
provide additional information to TxDOT personnel.
The following stages of the project will incorporate the literature and empirical
knowledge gained with the expertise of the engineers that are experience with intersection
remediation. The knowledge has been collected by thorough interview with districts experts and
is in the process of summarization. An expert system will be developed and will serve as a step-
by-step guidance on the process of designing the optimum solution. The expert system will have
a knowledge base that will include all the factors that will be developed in the guidelines to reach
the final decision.
92
REFERENCES
• AASHTO (1986). “Guide for Design of Pavement Structures.” American Association of State Highway and Transportation Officials, 444 North Capitol St., N.W., Suite 249, Washington, DC 20001.
• AASHTO (2001). “Guidelines for Geometric Design of Very Low-Volume Local Roads.” American Association of State Highway and Transportation Officials, 444 North Capitol St., N.W., Suite 249, Washington, DC 20001
• AASHTO (2002). “AASHTO Design Guide 2002 (NCHRP 1-37), The Mechanistic-Empirical Design Guide.” American Association of State Highway and Transportation Officials, 444 North Capitol St., N.W., Suite 249, Washington, DC 20001
• Abd El Halim, A.O. (1983). “Geogrid Reinforcement of Asphalt Pavements.” PhD Dissertation, University of Waterloo, Ontario, Canada.
• American Concrete Pavement Association (ACPA) (1998). “Whitetopping: State of the Practice.” Engineering Bulletin, Skokie, IL., EB210P
• Army TM 5-822-14 (1994). “Soil Stabilization for Pavements.” Department of the Army, the Navy, and the Air Force, Washington, DC.
• Asphalt Institute (AI) (1991). “Thickness Design-Asphalt Pavements for Highways and Streets.” Manual Series, No. 1, 2696 Research Park Drive, Lexington, KY 40511-8480
• Australian Asphalt Pavement Association (AAPA, 1999). “Bituminous Surfacing for Intersections on Light & Medium Flexible Pavements.” Advisory note 15, KEW Victoria 3101, Australia.
• Biddle, P.G. (1983). “Patterns of Soil Drying and Moisture Deficit in The Vicinity of Trees on Clay Soils.” Geotechnique, 33, Issue 2, pp.107-126.
• Biddle, P.G. (2001). “Tree Root Damage to Buildings.” ASCE Geotechnical Special Publication, 115, pp.1-23.
• Brown, E.R. and Cross, S. (1992). “A National Study of Rutting in Asphalt Pavement.” Proc. of AAPT, Vol. 61, 1992, p. 535-582.
• Buncher, M. (2002). “Designing Asphalt Pavements at Intersections.” Asphalt Review Magazine, Fall 2002 Issue, pp.14-15.
• Caltrans (2003). “Maintenance Technical Advisory Guide.” State of California Department of Transportation, Office of Pavement Preservation, Division of Maintenance, Sacramento, CA 95814
• Chen, L. and Tian, K. (1985). “The Effect of Vegetation Transpiration on the Deformation of High Void Ratio Expansive Soil Foundation.” Transportation Research Record 1032, pp.68-75.
• Chou, L. (Ed.) (1987) “Lime Stabilization: Reactions, Properties, Design and Construction” TRB State of the Art Report 5, Transportation Research Board, National Research Council, Washington DC.
• Cicoff, G.A. and Sprague, C.J. (1991). “Permanent Road Stabilization: Low-Cost Pavement Structures and Lightweight Geotextiles.” Transportation Research Record 1291. pp.294-310.
• Çokça, E. (2001). “Use of Class C Fly Ashes for the Stabilization of an Expansive Soil.” Journal of Geotechnical and Geoenvironmental Engineering, 127(7), 568-273.
93
• Cole, L., Mack, J. and Packard R. (1997). “Whitetopping and Ultra-Thin Whitetopping: The U.S. Experience.” Proceedings of the 8th International Symposium on Concrete Roads, Lisbon, Theme IV, pp. 203-217.
• Colorado Department of Transportation (CDOT) (2009). “Pavement Design Manual – Principles of Design for Flexible Pavement Intersections.” The Materials and Geotechnical Branch of the Colorado Department of Transportation, Denver, CO.
• Croft, J.B. (1967). “The Influence of Soil Mineralogical Composition on Cement Stabilization.” Geotechnique, vol. 17, pp.119–135, London, England.
• Epps, J. A. (1990). “Cold Recycled Bituminous Concrete Using Bituminous Materials.” NCHRP Synthesis of Highway Practice 160, TRB National Research Council, Washington DC.
• Fang, H. (2001) “Rational Approach to Rutting Rehabilitation Decisions”, PhD Dissertation, Purdue University, West Lafayette, IN
• FHWA (2002). “Life-Cycle Cost Analysis Primer.” Federal Highway Administration, Office of Asset Management (HIAM), U.S. Department of Transportation, 400 7th Street, SW, Room 3211, Washington, DC 20590
• Federation of Canadian Municipalities and Canadian National Research Council (2003). “Rut Mitigation Techniques at Intersections.” National Guide to Sustainable Municipal Infrastructure, Issue No. 1.0, Ottawa, Ontario, Canada.
• Ferguson, G. (1993). “Use of self-cementing fly ashes as a soil stabilization agent.” ASCE Geotechnical Special Publication No. 36, ASCE, New York, U.S.
• Giroud, J.P. and Han, J. (2004a). “Design Method for Geogrid-Reinforced Unpaved Roads. I. Development of Design Method.” Journal of Geotechnical and Geoenvironmental Engineering, pp.775-786.
• Giroud, J.P. and Han, J. (2004b). “Design Method for Geogrid-Reinforced Unpaved Roads. II. Calibration and Applications.” Journal of Geotechnical and Geoenvironmental Engineering, pp.787-797.
• Giroud, J.P. and Noiray, L. (1981). “Geotextile-Reinforced Unpaved Road Design.” Journal of Geotechnical Engineering Division, Proceedings of the ASCE Vol. 107, No. GT9, pp.1233-1254.
• Gurung, N. (2003). “A Laboratory Study on the Tensile Response of Unbound Granular base Road Pavement Model Using Geosynthetics.” Geotextiles and Geomembranes 21, pp.59-68.
• Hajj, E., Siddharthan, R., Sebaaly, P. and Weitzel, D. (2007). “Hot Mix Asphalt for Nevada’s Intersections.” Transportation Research Board 2007 Annual Meeting, Washington D.C.
• Hicks, R.G. (2002). “Alaska Soil Stabilization Design Guide.” Oregon State University, Department of Civil Engineering, Department of Transportation and Public Facilities, Research and Technology Transfer, FHWA-AK-RD-01-6B, Fairbanks, Alaska.
• Hicks, R. G., Seeds, S., and Peshkin D. (2000). “Selecting a Preventive Maintenance Treatment for Flexible Pavements.” Foundation for Pavement Preservation, 2025 M Street, NW Suite 800, Washington, DC 20036-3309
• Helstrom, C. L., Humphrey, D. N., and Labbe, J. M. (2007). “Performance and Effectiveness of a Thin Pavement Section Using Geogrids and Drainage Geocomposites in a Cold Region.” New England Transportation Consortium, Report No. NETCR60, University of Maine, Orono, Maine.
94
• Hopkins , T.C. and Sharpe, G.W. (1985) “Unstable Subgrade I-65, Hardin County” FSP 047-0065-091-0396, University of Kentucky Transportation Center, College of Engineering, Research Report UKTRP 85-9, Lexington, KY.
• Hopkins, T.C. and Beckham, T.L. (2000). “Influence of Clay Fraction on the Behavior of Soil Subgrades.” Proceedings, 5th International Symposium on Unbound Aggregates in Roads, Nottingham, UK.
• Hopkins, T.C., Sun, L. and Slepak, M. (2005). “Bearing Capacity Analysis and Design Of Highway Base Materials Reinforced with Geofabrics.” University of Kentucky Transportation Center, College of Engineering, Research Report KTC-05-21/SPR 238-02-1F, Lexington, KY.
• Hufenus R., Rueegger, R., Banjac, R., Mayor, P., Springman, S.M. and Brönnimann, R. (2006). “Full-Scale Field Tests on Geosynthetic Reinforced Unpaved Roads on Soft Subgrade.” Geotextiles and Geomembranes 24, pp.21-37.
• Illinois Department of Transportation (IDOT) (2002). “Pavement Design – Chapter Fifty-Four.” Bureau of Design and Environment, 2300 South Dirksen Parkway, Room 330, Springfield, Illinois 62764
• Kalcheff, I.V. and Tunnicliff, D.G. (1982). “Effects of Crushed Stone Aggregate Size and Shape on Properties of Asphalt Concrete.” Proc. of AAPT, Vol. 51.
• Kandhal, Prithvi S. (1998). “Hot Mix Asphalt for Intersections in Hot Climates.” National Center for Asphalt Technology, NCAT Report 98-06, Auburn University, 277 Technology Parkway, AL 36830.
• Kearney, E. J. and Huffman, J. E. (1999). “The Full Depth Reclamation Process.” National Research Council, Journal of the Transportation Research Board, No. 1684, pp. 203-209.
• Keller, G. and Sherar, J. (2003). “Low-Volume Roads Engineering Best Management Practices Field Guide.” United States Department of Agriculture (USDA) Forest Service, US Agency for International Development (USAID), 1400 Independence Av., Washington, DC.
• Koerner, R.M. (2005). “Designing with Geosynthetics.” Pearson Prentice Hall, 5th Ed., Upper Saddle River, NJ.
• Kota, P.B.V.S., Hazlett, D., and Perrin, L. (1996). “Sulphate-bearing soils: Problems with calcium-based stabilizers.” Transportation Research Record 1546, pp.62-69.
• Kwon, J., Tutumluer, E., Al-Qadi, I.L. and Dessouky, S. (2008). “Mechanistic Model Development and Response Validation for Geogrid Base Reinforced Flexible Pavements.” The First pan American Geosynthetics Conference & Exhibition, Cancun, Mexico.
• Little, D.N. (1999). “Evaluation of Structural Properties of Lime Stabilized Soils and Aggregates.” National Lime Association Publication, Summary of Findings, Vol. 1, Arlington, VA.
• Little, D.N., Males, E. H., Prusinski, J.R. and Stewart, B. (2000). “Cementitious Stabilization.” Transportation in the New Millennium: Perspectives from TRB Standing Committees, Committee on Cementitious Stabilization, Committee A2J01, TRB. National Research Council, Washington, DC.
• Liu, W., and Scullion, T. (2008). “PAVECHECK: Updated User’s Manual.” Texas Transportation Institute, Texas A&M University System, FHWA Report No. 5-4495-01-P1, Fort Worth, TX.
• Long-Term Pavement Performance Program (2005). “Distress Identification Guide.” Federal Highway Administration, North Dakota, U.S.
95
• Montanelli, F., Zhao, A.G. and Rimoldi, P. (1999). “Geosynthetic-Reinforced Pavement System: Testing & Design.” TENAX, <http://www.tenax.net/> (Nov., 2008)
• Natural Resources Conservation Service (NRCS) (2009) “Web Soil Survey.” United States Department of Agriculture, < http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm> (Dec., 17, 2009)
• Nelson, J.D. and Miller, J.D. (1992). “Expansive Soils: Problems and Practice in Foundation and Pavement Engineering.” John Wiley & Sons, Inc., New York: Wiley, 111 River Street, Hoboken, NJ 07030-5774
• Ontario Hot Mix Producers Association (OHMPA) (2004). “The ABCs of Pavement Preservation.” Issue 1.0, February 2004, 365 Brunel Road, Unit 4, Mississauga, ON L4Z 1Z5
• Ou, F, Ou. L. and Swarthout, C.D. (1986). “Cost-Estimating Model for Low-Volume Roads.” Transportation Research Record 1055. pp.51-56
• Prozzi, J. and Harrison, R. (2004). “Prioritizing Rural Infrastructure Needs.” Center for Transportation Research, the University of Texas at Austin, Texas Department of Transportation Research Report 0-4169-P3, Austin, TX.
• Puppala, A.J., Griffin, J.A., Hoyos, L.R. and Chomtid, S. (2004a). “Studies on Sulphate-Resistant Cement Stabilization Methods to Address Sulphate-Induced Soil Heave.” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 130, No. 4, pp. 391-402.
• Puppala, A.J., Katha, B. and Hoyos, L.R. (2004b). “Volumetric Shrinkage Strain Measurements in Expansive Soils Using Digital Imaging Technology.” Geotechnical Testing Journal, Vol. 27, No. 6
• Puppala, A.J., Wattanasanticharoen, E. and Punthutaecha, K. (2003). “Experimental Evaluations of Stabilization Methods for Sulphate-rich Expansive Soils.” Ground Improvement, Vol. 7, No. 1, pp. 25-35.
• Ravina, I. (1984). “The Influence of Vegetation on Moisture and Volume Changes.” The Influence of Vegetation on Clays, The Institution of Civil Engineers, Billings and Son Ltd., Great Britain, pp.62-68.
• Raymond, G. and Ismail, I. (2003). “The Effect of Geogrid Reinforcement on Unbound Aggregates.” Geotextile and Geomembranes 21, pp.355-380.
• Rollings, K.M. and Christie, R. (2002), “Pavement and Subgrade Distress-Remedial Strategies for Construction and Maintenance (I-15 Mileposts 200-217),” Utah DOT Research and Development Report No. UT-02.17, Salt Lake City, UT.
• Southern African Development Community (SADC) (1999). “Guideline on Low-volume Sealed Roads.” Pavement Design, Materials and Surfacing, Gaborone, Botswana.
• Sewell, M. and Marczak, M. (1997). “Using Cost Analysis in Evaluation.” USDA/CSREES, University of Arizona, <http://ag.arizona.edu/sfcs/cyfernet/cyfar/Costben2.htm>, (Feb., 2009)
• Smith, K.D., Yu, H.T. and Peshkin, D.G., (2002), “Portland Cement Concrete Overlays: State of the Technology Synthesis.” Federal Highway Administration (FHWA), FHWA-IF-02-045, Washington, DC.
• Snethen, D.R. (2001). “Influence of Local Tree Species on Shrink/Swell Behavior of Permian Clays in Central Oklahoma.” Expansive Clay Soils and Vegetative Influence on Shallow Foundations, Geotechnical Special Publication No. 115 (ed. C. Vipulanandan, M. B. Addison and M. Hasen), Reston: American Society of Civil Engineers, pp. 158-171.
96
• Steward, J., Williamson, R. and Mohney, J. (1977). “Guidelines for Use of Fabrics in Construction and Maintenance of Low-Volume Roads.” U.S. Department of Transportation, Federal Highway Administration, Report No. FHWA-TS-78-205, Washington DC.
• Suo, Z. and Wong, W. G. (2007). “Analysis of Fatigue Crack Growth Behavior in Asphalt Concrete Material in Wearing Course.” Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
• Terrel, R.L., Epps, J.A., Barenberg, E.J., Mitchell, J.K., and Thompson, M.R. (1979). “Soil Stabilization in Pavement Structures, A User’s Manual, Volume 2, Mix Design Considerations.” Federal Highway Administration, Report No. FHWA-IP-80-2, Washington DC
• TxDOT (2005a). “Guidelines for Modification and Stabilization of Soils and Base for Use in Pavement Structures.” Texas Department of Transportation, Construction Division, Materials and Pavements Section, Geotechnical, Soil and Aggregates Branch, Austin, TX.
• TxDOT (2005b). “Guidelines for Treatment of Sulfate-Rich Soils and Bases in Pavement Structures Soils.” Texas Department of Transportation, Construction Division, Materials and Pavements Section, Geotechnical, Soil and Aggregates Branch, Austin, TX.
• TxDOT (2006). “Pavement Design Guide.” Texas Department of Transportation, <http://onlinemanuals.txdot.gov/manuals/>, (Dec. 23, 2009)
• Thompson, M.R., (1966). “Lime Reactivity of Illinois Soils.” Journal of the Soil Mechanics and Foundations Division, ASCE, Vol. 92, No. SMS.
• Transit New Zealand (2007). “New Zealand Supplement to the Document, Pavement Design – A guide to the Structural Design of Road Pavements (AUSTROROADS, 2004).” Lampton Quay, Wellington, New Zealand.
• Tucker, R.L. and Poor, A.R. (1978). “Field Study of Moisture Effects on Slab Movements.” Journal of Geotechnical Engineer, ASCE, 104(4), pp. 403-415.
• Tutumluer, E. and Kwon, J. (2005). “Evaluation of Geosynthetics use for Pavement Subgrade Restraint and Working Platform Construction.” Proc. of 13th Annual Great Lakes Geotechnical/Geoenvironmental Conference on Geotechnical Applications for Transportation Infrastructure, Milwaukee, WI.
• Walker, D. and Buncher, M. (1999), “Intersection Strategy (Part 1-3)”, Asphalt Magazine, summer 1999, Lexington, KY.
• Ward, W.H. (1953). “Soil Movements and Weather” Proceedings of 3rd International Conference Soil Mechanics, 2, Zurich, Switzerland, pp.477-481.
• Wesseldine, M.A. (1982). “House Foundation Failures Due To Clay Shrinkage Caused by Gum Trees.” Transactions, Institution of Professional Engineers, N.Z. March, CE9(1).
• White, D.J., Harrington, D. and Thomas, Z. (2005a). “Fly Ash Soil Stabilization for Non-Uniform Subgrade Soils, Volume I: Engineering Properties and Construction Guidelines.” Iowa Highway Research Board, Report No. IHRB Project TR-461; FHWA Project 4, Ames, IA.
• White, D.J., Harrington, D. and Rupnow, T. (2005b). “Fly Ash Soil Stabilization for Non-Uniform Subgrade Soils, Volume II: Influence of Subgrade Non-Uniformity on PCC Pavement Performance.” Iowa Highway Research Board, Report No. IHRB Project TR-461; FHWA Project 4, Ames, IA.
• Yoder, E.J., and Witczak, M.W. (1975), “Principles of Pavement Design” 2nd ed. John Wiley & Sons, Inc., New York, 1975.
97
APPENDIX A: TXDOT RESEARCH PROJECT 0-5566 QUESTIONNAIRE
Questionnaire for TxDOT Research Project 0-5566 Strategies to Improve and Preserve Flexible Pavement at Intersections
Many rural intersections originally constructed with thin untreated flexible base and hot mix or a two-course surface treatment experience severe pushing, shoving and rutting. These failures cause an extremely rough surface that can cause damage to small vehicles and potentially cause motorists to loose control of their vehicle. Pavement sections constructed with the same materials adjacent to the intersection usually perform adequately until the approach (approximately 150 ft in advance) of the intersection and in the intersection itself when the failures become apparent. TxDOT has initiated a new project to understand the mechanisms of intersection pavement failures and determine the best practices to minimize the failures at existing intersection pavements. The outcome of this project should reduce the frequency of maintenance needed at rural intersections. This project would also determine how the mechanisms causing the surface failures at intersections can be mitigated through design and construction modifications. Please help us to identify the intersections in your district that can be used for this project by answering the following questions.
98
TxDOT Research Project TX-0-5566 Distress Questionnaire
District Name:________________________ Contact Person: ________________________________ (1) Do your pavements experience distress at the intersections of low volume roads? (Yes / No ) (2) If yes, what percentage of the intersections experiences any type of distress? _______________% (3) Approximately what percentages of distressed intersections experience the following distress severity?
(total for the three categories should be 100%) Low Severity (___%) Medium Severity (____%) High Severity (___%) (4) What distress types are common at your intersections on low volume roads? (check all that apply)
Rutting, Shoving, Cracking, Pushing, Other ________________________________________ (5) If rutting is an issue at intersections, please select: (check all that apply)
a) Probable cause:
Inadequate structures - specify (ex. weak subgrade)_______________________________________
Construction quality - please specify (ex. site preparation)__________________________________
Traffic - please specify (ex volume, slow moving, channeled)_______________________________
Environmental condition - please specify (ex. moisture, temperature)_________________________
Inadequate drainage________________________________________________________________
Subgrade type - please specify (ex. clayey, sandy)________________________________________
Other___________________________________________________________________________
(6) If shoving is an issue at intersections, please select: (check all that apply)
a) Probable cause: Inadequate structures - specify (ex. weak subgrade)_______________________________________
Construction quality - please specify (ex. site preparation)__________________________________
Traffic - please specify (ex volume, slow moving, channeled)_______________________________
Environmental condition - please specify (ex. moisture, temperature)_________________________
Subgrade type - please specify (ex. clayey, sandy)________________________________________
Other___________________________________________________________________________
99
TxDOT Research Project TX-0-5566 Distress Questionnaire
(7) If cracking is an issue at intersections, please select: (check all that apply)
a) Probable cause: Inadequate structures - specify (ex. weak subgrade)_______________________________________
Construction quality - please specify (ex. site preparation)__________________________________
Traffic - please specify (ex volume, slow moving, channeled)_______________________________
Environmental condition - please specify (ex. moisture, temperature)_________________________
Subgrade type - please specify (ex. clayey, sandy)________________________________________
Other___________________________________________________________________________
(8) If pushing is an issue at intersections, please select: (check all that apply)
a) Probable cause: Inadequate structures - specify (ex. weak subgrade)_______________________________________
Construction quality - please specify (ex. site preparation)__________________________________
Traffic - please specify (ex volume, slow moving, channeled)_______________________________
Environmental condition - please specify (ex. moisture, temperature)_________________________
Subgrade type - please specify (ex. clayey, sandy)________________________________________
Other___________________________________________________________________________
(9) (Other) _______________________ is an issue at intersections, please select: (check all that apply)
a) Probable cause: Inadequate structures - specify (ex. weak subgrade)_______________________________________
Construction quality - please specify (ex. site preparation)__________________________________
Traffic - please specify (ex volume, slow moving, channeled)_______________________________
Environmental condition - please specify (ex. moisture, temperature)_________________________
Subgrade type - please specify (ex. clayey, sandy)________________________________________
Other___________________________________________________________________________
100
TxDOT Research Project TX-0-5566 Distress Questionnaire
(10) Please fill the table below regarding solutions you typically use to remedy each distress and provide typical performance life of each remedy.
Distress Current solutions you typically use to remedy this problem.
Performance of the remediation
Rutting
□ Hot Mix Overlay, □ Concrete Overlay (White Topping and Bonded PCC) □ Preservation (ex. Chip Seal) □ Rehabilitation (ex. Mill & Fill) □ Reconstruction □ Full Depth Reclamation □ Other _____________________
□ Less than 1 year □ 1 to 3 years □ 3 to 10 years □ More than 10 years
Shoving
□ Hot Mix Overlay, □ Concrete Overlay (White Topping and Bonded PCC) □ Preservation (ex. Chip Seal) □ Rehabilitation (ex. Mill & Fill) □ Reconstruction □ Full Depth Reclamation □ Other _____________________
□ Less than 1 year □ 1 to 3 years □ 3 to 10 years □ More than 10 years
Cracking
□ Hot Mix Overlay, □ Concrete Overlay (White Topping and Bonded PCC) □ Preservation (ex. Chip Seal) □ Rehabilitation (ex. Mill & Fill) □ Reconstruction □ Full Depth Reclamation □ Other _____________________
□ Less than 1 year □ 1 to 3 years □ 3 to 10 years □ More than 10 years
Pushing
□ Hot Mix Overlay, □ Concrete Overlay (White Topping and Bonded PCC) □ Preservation (ex. Chip Seal) □ Rehabilitation (ex. Mill & Fill) □ Reconstruction □ Full Depth Reclamation □ Other _____________________
□ Less than 1 year □ 1 to 3 years □ 3 to 10 years □ More than 10 years
Others (specify)
______________________
□ Hot Mix Overlay, □ Concrete Overlay (White Topping and Bonded PCC) □ Preservation (ex. Chip Seal) □ Rehabilitation (ex. Mill & Fill) □ Reconstruction □ Full Depth Reclamation □ Other _____________________
□ Less than 1 year □ 1 to 3 years □ 3 to 10 years □ More than 10 years
(12) Do you mind if we contact you for further information? (Yes / No) If you do not mind, please provide the following: Telephone number: ______________________ Email: __________________________________________
101
APPENDIX B: SUMMARY OF QUESTIONNAIRE
102
Table B.1: Summary of Causes of Rutting for each District
Districts Inadequate Structures
Const. Quality Traffic
Environ. Conditions
Inadequate Drainage
Subgrade Type Other
Abilene X X Atlanta X X X X Brownwood X X Bryan Ft. Worth X X Ft. Worth2 X X Ft. Worth3 X X X Houston X X X X X X Lubbock X X X X X Lubbock2 X X X X X Lubbock3 X X X X X X Lufkin Odessa Paris X Pharr X San Antonio X X X
Table B.2: Summary of Causes of Shoving for each District
Districts Inadequate Structures
Const. Quality Traffic
Environ. Conditions
Inadequate Drainage
Subgrade Type Other
Abilene X X Atlanta Brownwood X X Bryan X X X X Ft. Worth Ft. Worth2 X X Ft. Worth3 X X Houston X X X Lubbock X X X Lubbock2 X X X X Lubbock3 X X X X X X X Lufkin Odessa X Paris X Pharr San Antonio X X X
103
Table B.3: Summary of Causes of Cracking for each District
Districts Inadequate Structures
Const. Quality Traffic
Environ. Conditions
Inadequate Drainage
Subgrade Type Other
Abilene X X Atlanta X X X Brownwood X X Bryan X X X Ft. Worth Ft. Worth2 X Ft. Worth3 X X X Houston X X Lubbock X X X Lubbock2 X X X Lubbock3 X X X X X X Lufkin X Odessa Paris X Pharr San Antonio X X X X
Table B.4: Summary of Causes of Pushing for each District
Districts Inadequate Structures
Const. Quality Traffic
Environ. Conditions
Inadequate Drainage
Subgrade Type Other
Abilene Atlanta Brownwood X X Bryan X X X Ft. Worth Ft. Worth2 X X Ft. Worth3 X X X Houston X X X Lubbock X X Lubbock2 X X X X X Lubbock3 X X X X X X X Lufkin Odessa X Paris X Pharr X San Antonio X X X X X
104
Table B.5: Summary of Causes of Other Distresses for each District
Districts Inadequate Structures
Const. Quality Traffic
Environ. Conditions
Inadequate Drainage
Subgrade Type Other
Abilene Atlanta X Brownwood Bryan X Ft. Worth Ft. Worth2 Ft. Worth3 X Houston Lubbock Lubbock2 Lubbock3 X X X X X X Lufkin Odessa Paris Pharr San Antonio X
Table B.6: Summary of Remediation Strategies for Rutting
Districts
Hot Mix Blade
Overlay Concrete Overlay Preser. Rehab. Reconst.
Full Depth Reclamation Other
Abilene X X X Atlanta X X Brownwood X Bryan Ft. Worth X X Ft. Worth2 X X Ft. Worth3 X X Houston X X X Lubbock X X X X X X Lubbock2 X X Lubbock3 X X Lufkin X Odessa Paris X X Pharr X X San Antonio X X X
105
Table B.7: Summary of Remediation Strategies for Shoving
Districts
Hot Mix Blade
Overlay Concrete Overlay Preser. Rehab. Reconst.
Full Depth Reclamation Other
Abilene X X X Atlanta X X X Brownwood X Bryan X Ft. Worth Ft. Worth2 X X Ft. Worth3 X Houston X X X Lubbock X X X Lubbock2 X X X Lubbock3 X X Lufkin X Odessa X Paris X X Pharr San Antonio X X X
Table B.8: Summary of Remediation Strategies for Cracking
Districts
Hot Mix Blade
Overlay Concrete Overlay Preser. Rehab. Reconst.
Full Depth Reclamation Other
Abilene X X X X Atlanta X X X Brownwood X Bryan X Ft. Worth Ft. Worth2 X X Ft. Worth3 X X Houston X X X X Lubbock X X X Lubbock2 X X Lubbock3 X X Lufkin X Odessa Paris X X X Pharr San Antonio X X X
106
Table B.9: Summary of Remediation Strategies for Pushing
Districts
Hot Mix Blade
Overlay Concrete Overlay Preser. Rehab. Reconst.
Full Depth Reclamation Other
Abilene Atlanta X X X Brownwood X Bryan X Ft. Worth Ft. Worth2 X X Ft. Worth3 X Houston X X X Lubbock X X X X Lubbock2 X X Lubbock3 X Lufkin X Odessa X Paris X X X Pharr X X San Antonio X X X X
Table B.10: Summary of Remediation Strategies for Other Distresses
Districts
Hot Mix Blade
Overlay Concrete Overlay Preser. Rehab. Reconst.
Full Depth Reclamation Other
Abilene Atlanta X X Brownwood Bryan X Ft. Worth Ft. Worth2 Ft. Worth3 Houston Lubbock Lubbock2 Lubbock3 X X Lufkin Odessa Paris Pharr San Antonio
107
APPENDIX C: EXCEL SPREADSHEET INTERFACE MANUAL
108
The Intersection Repair Method Selection Spreadsheet was developed in Microsoft Excel
in order to identify the proper remediation methods for flexible pavements at intersections and to
perform the Life Cycle Cost Analysis (LCCA) to obtain the most economical alternative.
Namely, this program is focused on helping the user’s decision-making in an interactive form.
The spreadsheet requires no installation, and since it doesn’t contain several macros no
extra activities have to be carried out. The software may be used for the following purposes:
• Finding the appropriate repair alternatives for a given flexible pavement structure and
traffic loading scenario.
• LCCA variables determination such as Initial Cost, Present Value, Total Present Value
and Salvage Value.
• LCCA graphs for comparison of the recommended repair alternatives.
• Daily ESAL determination based on the average AADT (Average Annual Daily Traffic)
throughout the extension of the analysis period, the correlation for the number of 18 kip
(80 kN0 single-axle load applications per truck, and the percentage of traffic traveling per
lane on each direction.
The spreadsheet consists of the following 6 sections:
1. General Project Information
2. Analysis Options
3. Traffic Conditions
4. Evaluate Existing Pavement Condition
5. Repair Alternatives
6. Life Cycle Cost Analysis
C.1 SECTION 1: GENERAL PROJECT INFORMATION
This section is mainly for the documentation of the site. Figure C.1 shows the initial
section, the empty boxes are supposed to be filled with the project information, such as project
109
name, county, district, roads, control, section, job, user name, and date of the analysis. At the
right side of each box an example is provided to orientate the user.
Figure C.1 – Section No. 1 General Project Information.
C.2 SECTION 2: ANALYSIS OPTIONS
The information provided in this section is used to calculate the costs and allow
performing the LCCA. The first item on the list is the Area to be Repaired which has to be given
in square yards. This item is essential to calculate the Initial Cost that will be later used for
obtaining the Present Value, and so the Salvage and Total Present Values. The Beginning of
Analysis Period is the year in which the construction is planned to start, and it will only be
employ on the comparison LCCA graphs. The Analysis Period is used to economically compare
the recommended alternatives under the same period by adding up all the rehabilitation and
maintenance costs required within that period for each alternative, and subtracting the Salvage
Value if any. Moreover, the Analysis Period is also used to compute the factor that brings the
future costs to present worth. Likewise, the Discount Rate is utilized in the same formula for
finding the Present Value of the amount to be spent in the future, and it is usually around 4%.
Figure C.2 shows an example of Section 2 filled with typical values.
110
Figure C.2 – Section No. 2 with Analysis Options Input.
C.3 SECTION 3: TRAFFIC CONDITIONS
The spreadsheet represents an economization tool by recommending low cost alternatives
that would perform at their best on low volume roads. The information obtained from this
section is used to classify the traffic volume of the intersection.
The classification is based on a differentiating value of 150 daily ESALs. If the traffic is
under 150 daily ESALs then the intersection is considered as low volume and the low cost
alternatives will be considered in the evaluation, otherwise the intersection will be considered as
high volume and the recommended alternatives will be the typical for high volume roads. Figure
C.3 illustrates the traffic conditions input section, where 5 boxes have to be filled to calculate the
daily ESALs, or if available just directly input the daily ESALs. The first box is for the Average
Annual Daily Traffic (AADT) during the year of construction, while the second box is for the
estimated AADT at the end of the analysis period, these two values with the purpose of
calculating an average AADT during the extension of the analysis period. The Combination of
Trucks as Percentage of AADT is necessary to calculate the number of heavy vehicles and then
be multiplied by the Truck Factor which is the correlation for the number of 18 kip (80 kN)
single-axle load applications per truck. Finally the Lane Distribution Factor (LDF) represents
the percent of traffic traveling per lane on each direction, since rural roads consist of one lane per
direction a value of 1.0 is recommended. Equation C.1 is used by the spreadsheet to calculate the
daily ESALs.
( )( )( )( )5.02
LTTAADTAADT
ESALDaily ffi
⎟⎟⎠
⎞⎜⎜⎝
⎛ += (E.1)
111
where:
AADTi = Average Annual Daily Traffic during construction year
AADTf = Average Annual Daily Traffic projected at the end of analysis period
T = Truck Percentage
Tf = Truck Factor
L = Lane Distribution Factor
Figure C.3 – Section No. 3 with Traffic Conditions Input.
C.4 SECTION 4: EVALUATE EXISTING PAVEMENT CONDITION
Section 4 is to identify the problem based on visual identification, classification and
severity of the distresses and the failing layer of the pavement structure. It consists of three
selection boxes that have to be filled in order each time.
Figure C.4 – Section No. 4 for the Evaluation of the Existing Pavement.
C.5 SECTION 5: REPAIR ALTERNATIVES
This section provides two tables. The first table presents all the possible repair
alternatives for the problem identified (in this case based on the answers from Figure C.4), both
maintenance and rehabilitation options. The “Recommended” and “May be Appropriate” are
112
differentiated by highlighting the first ones in green and the second ones in yellow (a color
legend is provided). The same table provides default values for materials and construction costs,
and life expectancies for each alternative, which might be adjusted by the user’s own experience
or knowledge. All these default values were collected from the literature and gathered together
in the “Cost & Life” sheet that will be described shortly.
Figure C.5 – Section No. 5 with all the Possible Alternatives.
The second table separates the rehabilitation alternatives from the maintenance
alternatives, allowing the user to select from a box a maintenance method to be performed within
the life of each of the rehabilitation alternatives. The user might choose the same, different or
not maintenance at all for each of rehabilitation treatments. This table also provides default
values for materials and construction costs, and life expectancies of each maintenance alternative
selected, also allowing the user to modify such values.
113
Figure C.6 – Section No. 5 Table for Maintenance Method Selection.
C.6 SECTION 6: LIFE CYCLE COST ANALYSIS
LCCA is used to quantify the total economic value of a project over its life. The main
purpose of LCCA is to evaluate the long-term repercussions of initial pavement design on the
future cost of maintenance necessary to maintain an acceptable service level for a specified time.
The parameters used for the LCCA include Initial Costs, future maintenance costs over the life of
the project, and Salvage Value at the end of the analysis period. This research is focused on rural
road intersections with low daily traffic and also, in many cases user cost is not readily available.
Therefore user’s costs (user delay costs, vehicle operating costs, and crash costs) and the
construction activity timing were omitted from the analysis.
The first step is to establish the alternatives that will accomplish the structural and
performance objectives of the project. The analysis period is essential for the LCCA to compare
the recommended alternatives economically. In addition, it is necessary that all alternatives are
under the same analysis period. The activity timing has to be determined for the initial and future
activities involving on each project design alternative. All the related costs for construction and
maintenance throughout the analysis period for each alternative have to be included in the
analysis, as well as the effects of the construction and maintenance activities on users. For all the
rehabilitation alternatives the option of selecting a maintenance method to be performed within
the life of the rehabilitation is provided. TxDOT (2006) recommends that the selected
rehabilitation design strategy for flexible pavements should provide a minimum initial
performance period of 8 years before an overlay is required. Therefore, when comparing
rehabilitation alternatives with maintenance in between a period of 8 years is recommended
114
before the first maintenance. The expected life of the maintenance method selected is used to
determine the timing between maintenances under the analysis period. With the predicted
schedule of activities all the costs during the analysis period are converted into present dollars by
using a technique known as “discounting”, and are finally all added up for each alternative.
The cost of each alternative is easily calculated with the total area to be repaired by the
unit cost of construction and materials provided. While the initial cost remains the same, all the
future costs (including salvage value) are adjusted to present value with Equation C.2 by using
the discount factor. Salvage value is calculated as the remaining value of the last maintenance
when it still has a remaining life over the analysis period. Salvage is also adjusted to present
value and is subtracted from the cost summation. The equations used to calculate the present
value or discounting are the following:
( ) ⎟⎟
⎠
⎞⎜⎜⎝
⎛
+×=
knralueVFutureValueresentP
11
(C.2)
( )∑ ⎟⎟
⎠
⎞⎜⎜⎝
⎛
+×+=
knrValueFutureCostInitialValueresentPTotal
11
(C.3)
where:
r = real discount rate
n = number of years in the future when the cost will be incurred
The lowest of the cost summations of each alternative can be determined as the most
cost-effective alternative.
The table in Figure C.7 displays the results of the Life Cycle Cost Analysis, Total Present
Values, Initial Costs, and Routine Maintenance Costs within the analysis period. The option of
ranking the alternatives by “Initial Cost” or “Total Present Value” is given by a selection box.
The alternatives maintain the color label to differentiate between the recommended and may be
appropriate alternatives.
115
Total Present Value list contains the addition of the discounted future values, including
rehabilitations and maintenances throughout the analysis period, and the subtraction of the
Salvage Value they might have left. Meanwhile, the Initial Cost and Routine Maintenance lists
values are not adjusted at all.
Figure C.7 – Section No. 6 with Ranked Cost Results.
Furthermore, all the alternatives are compared based on their Present Value in a graph on
Figure C.8. Again, the values for cost are adjusted to present value by using the discount rate and
the analysis period.
116
Figure C.8 – Section No. 6 All Alternative Present Value Comparison Graph.
The graph on Figure C.9 plots the costs as well as the activity timing throughout the
analysis period of the most economical remediation alternative; the green values represent
rehabilitation and maintenance costs while the red bar represents the salvage value of the
construction at the end of the analysis period.
Figure C.9 – Section No. 6 LCCA Plot for the Most Economical Alternative.
117
Figure C.10 shows the graph that allows the user to visually compare the computed
LCCA of any alternative with the most economical one shown on the previous graph, by
selecting the comparative treatment method on a selection box. Same concept applies as in
Figure C.10, the green values represent rehabilitation and maintenance costs while the red bar
represents the salvage value of the construction at the end of the analysis period.
Figure C.10 – Section No. 6 LCCA Plot for a Selected Alternative.
C.7 COST AND LIFE EXPECTANCY SHEET
The table shown on Figure C.11 is found in the “Cost & Life” sheet of the program, and
it provides default values, gathered in the literature, for construction and maintenance costs, and
expected life for each of the remediation and maintenance alternatives. Values in this table may
be adjusted by the user. Three empty spaces are left for the user to add the costs and life
expectancies of additional alternatives.
118
Figure C.11 – Cost and Life Expectancies for Each Alternative Table.
C.8 REMEDIATION METHODS TABLE SHEET
The table in Figure C.12 is found in the “Remediation Table” sheet of the program. Such
table combines the predominant distresses at intersections with the recommended remediation
alternatives and provides recommendations on how effective each remediation may be to solve
119
each of the distresses. The table contains a legend allowing to identify when an alternative is
recommended, may be appropriate, not recommended, or simply doesn’t apply to the defined
problem. The recommendations are based on literature but may be adjusted to the user’s own
experience and knowledge, as long as the same labels are used. Also three empty spaces are left
for the user to include and considerate additional alternatives in the analysis. The
recommendation effectiveness of the additional alternatives to solve each distress should be
added by the users.
Figure C.12 – Remediation Methods for Different Distresses Table.
120
C.9 PROGRAM DECISION TREE
Figure C.13 is found in the “Program Decision Tree” sheet of the program. The decision
three is a tool that may help the user to follow the program’s steps. Even-though, the decision
tree is based on the Remediation Methods Table, it doesn’t represent any thing else but a flow
diagram.
Figure C.13 – Decision Tree.
C.10 LCCA SHEET
The table shown on Figure C.14 is found in the “LCCA” sheet of the program. This table
illustrates in detailed the calculated Initial Costs, Total Present and Salvage Values for the
chosen alternatives, coupled with future maintenance costs over the life of the project. The Cost
121
column presents the costs in future value, while the Present Value column displays them in
present worth. Here, the Beginning of Analysis Period is particularly used as the starting year of
the analysis period. In order to differentiate costs from positive values (Salvage Value) colored
numbers were used. In essence, black numbers represent cost, while red numbers stand for
Salvage Value.
Figure C.14 – LCCA Table.
C.11 ESAL TABLES SHEET
The tables shown on Figure C.15 are found in the “ESAL Tables” sheet of the program.
The Combination of Trucks as Percentage of AADT, Truck Factor and Lane Distribution Factor
Tables work together in Section No. 3 in order to find the value of Daily ESALs at the
intersection. More importantly, the Daily ESALs value is needed to classify the intersection into
low or high volume road, and then obtain the appropriate alternatives that will achieve the
122
structural and performance objectives of the project. Section No. 3 has default values of .52 and
1.00 for the Truck Factor and Lane Distribution Factor respectively. In addition, Section No. 3
includes hyperlink such tables for the user to modify the defaulted values.
Figure C.15a – Combination of Trucks as Percentage of AADT.
Figure C.15b – Truck Factor.
123
Figure C.15c – Lane Distribution Factor.
C.12 COMMON DISTRESSES AND REMEDIATION STRATEGIES SHEETS
The table shown on Figure E.16 is found on one of the several common distresses sheets
of the program. As stated on Section No. 4, the Intersection Repair Method Selection
Spreadsheet establishes its problem identification based on visual aids. As consequence, sections
where the common distresses are summarized were added. The common distresses synopsis
includes a brief description for each distress, the distresses causes, preventive and overall
solutions, and finally the rehabilitation alternatives. To end with, the common distresses sheets
will also have pictures showing the severities that the distresses might experience.
124
Figure C.16 – Common Distress Sheet for Shoving/Corrugation.
The table shown on Figure C.16 is found on one of the several common remediation
strategies sheets of the program. Similarly, sections where the remediation strategies are
summarized were also added. The remediation strategies synopsis includes a brief description of
125
each product, the typical traffic range, life expectancies, unit prices, appearance, advantages and
limitations. Finally, the remediation strategies sheets will also have pictures of the remediations.
Figure C.17 – Common Remediation Strategies for Microsurfacing.
126
APPENDIX D: REMEDIATION STRATEGIES
127
Remediation strategies divide into two categories: (1) Preventive Maintenance
Treatments which are low-cost treatments that retard deterioration of the pavement, maintain or
improve the functional condition of the roadway, and extend the pavement's service life when
applied on suitable candidates, and (2) Rehabilitations which repair the condition of the existing
pavement structure.
MICROSURFACING
The main use of micro-surfacing materials is for pavement preservation as a part of a
program of periodic surfacing before distresses appear. Micro-surfacing is a mixture of asphalt
emulsion, graded aggregates, mineral filler, water and other additives. The mixture is made and
placed on a continuous basis using a travel paver (Slurry Surfacing Machine). The travel paver
meters the mix components in a predetermined order into a pug mill. The typical mixing order is
aggregate followed by cement, water, the additive and the emulsion. Distress modes that can be
addressed using micro-surfacing include:
• Raveling: Loose surfaces or surfaces losing aggregate may be resurfaced using slurry
seals or micro-surfacing.
• Oxidized pavement with hairline cracks: These surfaces may be resurfaced using slurry
seals or micro-surfacing.
• Rutted pavements: Deformation resulting from consolidation of the surfacing only.
Rutting due to base failure of significant plastic deformation of the HMA cannot be
treated except as a temporary measure.
• Rough pavements with short wavelength: These irregularities may be treated with micro-
surfacing, provided the frequency of the irregularities is shorter than the spreader box
width.
Distress modes that cannot be addressed using micro-surfacing include:
• Cracking (including reflection cracking)
• Base Failures of any kind
128
• HMA Layers that exhibit plastic shear deformation
Micro-surfacing will not alleviate the cause of these distresses. As a result, the distresses will
continue to form despite the application of a slurry surfacing.
FOG SEAL
According to the Asphalt Emulsion Manufacturers Association (AEMA) a fog seal is a
light spray application of dilute asphalt emulsion used primarily to seal an existing asphalt
surface to reduce raveling and enrich dry and weathered surfaces. A fog seal is made to coat,
protect, and rejuvenate the existing asphalt binder. The addition of asphalt will also improve the
waterproofing of the surface and reduce its aging susceptibility by lowering permeability to
water and air. To achieve this, the fog seal material (emulsion) must fill the voids in the surface
of the pavement. Therefore, during its application it must have sufficiently low viscosity so as to
not break before it penetrates the surface voids of the pavement. This is accomplished by using a
slow setting emulsion that is diluted with water. Emulsions that are not adequately diluted with
water may not properly penetrate the surface voids resulting in excess asphalt on the surface of
the pavement after the emulsion breaks, which can result in a slippery surface.
CRACK SEAL
Crack sealing and filling prevent the intrusion of water and incompressible materials into
cracks. The methods vary in the amount of crack preparation required and the types of sealant
materials that are used. Crack sealing is the placement of materials into working cracks. Crack
sealing requires thorough crack preparation and often requires the use of specialized high quality
materials placed either into or over working cracks to prevent the intrusion of water and
incompressible materials. Crack sealing is generally considered to be a longer-term treatment
than crack filling. The pavement structure should be sound and cracks are only treated when
greater than 1/4in. or up to 1in. (Caltrans, 2003)
129
SAND SEAL
A sand seal is a thin asphalt surface treatment constructed by spraying a bituminous
binding agent and immediately spreading and rolling a thin fine aggregate (i.e. sand or
screenings) cover. A sand seal is basically the same as a chip seal except that finer aggregate is
used in the cover. Application of this sealer fills cracks and seals the surface against damage
from water, sunlight, gas and oil. Aggregates help make the sealed surface less slippery when
wet.
This sand seal is intended to be used on pavements that have lost some of their matrix,
and it is desirable for tightening the pavement texture and reducing raveling. Blend of heavy
mineral fillers and fine aggregates works well on large areas of fatigue cracking. Typical
AADT<400 when placed on aggregate base. Typical AADT<2,000 when placed on existing
HACP.
SLURRY SEAL
Slurry seal is a mixture of emulsified asphalt oil, rock, water, and additives such as
aluminum sulfate, Portland cement, lime, latex or carbon black. Which additives are used
depends on many factors including location, condition of surface, and the type of surface. All
these factors should be considered when the laboratory designs a mix. Slurry Seals are
treatments that provide pavement sealing and pavement texture but are not appropriate to resolve
structural pavement deficiencies. These systems are well suited as a preventive maintenance
treatment to extend the life of structurally sound low traffic volume pavements.
CHIP SEALS
Chip sealing is the application of a bituminous binder immediately followed by the
application of an aggregate. The aggregate is then rolled to embed it into the binder. Multiple
layers may be placed and various binder and aggregate types can be used to address specific
distress modes or traffic situations. Polymer-Modified Emulsion (PME) chip seals are normally
not suitable for intersections or high stress areas. Conventional chip seals are used on
130
structurally sound pavements with minimal cracking. Deformation, rutting and shoving cannot
be addressed with chip seals of any kind.
HOT IN-PLACE RECYCLING (HIPR)
This rehabilitation technique is meant to address asphalt concrete surface distress and
texture issues only, therefore the underlying base layers must offer adequate support.
The HIPR process involves recycling the existing asphalt surface layer by heating,
scarifying, and adding a recycling agent. There are three basic HIPR processes:
1. Heater-scarification - heating, scarifying, rejuvenating, leveling, reprofiling, and
compacting.
2. Repaving - heating, scarifying, rejuvenating, leveling, laying a new hot mix layer,
reprofiling, and compacting.
3. Remixing - heating, scarifying, rejuvenating, mixing (adding a new hot mix), leveling,
reprofiling, and compacting.
Pavements with delaminations, especially saturated delaminations, in the top 2in. should not be
considered for HIPR projects. Also, the state of practice does not recommend pavements that
have been rutted, heavily patched, or chip-sealed as good candidate projects. Typically, hot in-
place recycling operations are conducted when the ambient air temperature is 50ºF and rising,
but 2004 specifications cite a minimum surface temperature for hot mix asphalt (HMA)
placement of 60ºF. An additional overlay may be placed over the recycled surface if additional
structural strength is needed as in the case of the repaving process. An equivalent alternative
strategy is to mill 1in. of the existing top layer and place back 2in. Up to 30% RAP may be
allowed in the new 2in. overlay. (TxDOT, 2006)
COLD IN-PLACE RECYCLING (CIPR)
As with the hot in-place process, this rehabilitation technique is meant to address distress
within the bituminous portion of the pavement structure, but can reach as deep as 4 to 6in.
Therefore, the base must also be sound, with repairs made to locations that have failed or show
131
potential for failure. The process also involves a specialized train with a cold milling machine,
crushing/screen unit, and mixing unit that is capable of reclaiming the old asphalt, crushing
(screening and sizing) the RAP, and mixing the RAP with virgin aggregate (if necessary) and
emulsion. Coring of the existing ACP surface is necessary to determine the material properties
of the existing asphalt pavement to properly design proportions of virgin aggregate, emulsion
and rejuvenator, if necessary. Cores are also inspected for the presence of variations in the
pavement layers, delaminations and whether voids are saturated. The industry does not
recommend pavements that have been rutted, heavily patched, or chip-sealed as good candidate
projects. Generally, a seal coat or additional overlay will be required after adequate curing since
the cold re-processed mix has higher void ratios and is more difficult to compact than hot mix.
(TxDOT, 2006)
HMA & RECYCLED ASPHALT SHINGLES (RAS) OVERLAY
Special specifications for Hot Mix Asphalt concrete pavement containing reclaimed
roofing shingles are in TxDOT Item 3028
PCC OVERLAY (THICK)
Applying a concrete overlay on a HMA surfaced pavement may be a viable rehabilitation
strategy under certain circumstances. Where existing distress in an HMA-surfaced structure is
confined to the HMA itself (mix rutting, shoving, washboarding, cracking), but otherwise the
existing substructure is sound, a concrete overlay can offer a durable replacement surface. These
circumstances may present themselves at intersections or along open sections of highway.
Design can be for jointed or continuously reinforced concrete pavement (CRCP) overlays.
(TxDOT, 2006)
ULTRA-THIN WHITETOPPING
Ultrathin whitetopping use slabs from 2.0 to 4.0in. thick that are placed on an HMA
surface that has been milled or otherwise prepared to enhance the bond. Any concrete overlay
thinner than 4.0” is not currently allowed under TxDOT guidelines. This may restrict the use of
132
concrete overlays at certain curb and gutter intersections where vertical profile may not allow
direct placement on top of the existing HMA structure, and milling to the appropriate depth may
leave insufficient support. (TxDOT, 2006)
FULL DEPTH RECLAMATION
This rehabilitation procedure entails pulverizing the old pavement structure, blending in a
stabilizing agent, compacting, adding additional material, and resurfacing. This procedure is
meant to address deep structural problems ranging to depths as great as 12in. in the existing
structure. This is the practical limit of recycler cut-in and subsequent compaction of the recycled
layer. Deeper problems must be addressed by temporary storage such as windrowing removed
material in the right of way (ROW) or otherwise moving existing material off site. Efficiency is
improved by using a specialized train to reprocess the existing structure. New base and surfacing
is then applied to provide appropriate additional structure, ride quality, skid, weatherproofing,
etc. (TxDOT, 2006)
133
APPENDIX E: CORE SUMMARIES FROM INTERSECTION OF SH49 AND SH155
134
Core # 1 IWP Thickness, in 1.9 Location SH 155 South bound 500ft north Modulus 319 ksi Asphalt Content 8.57 % Notes
Gradation:
Size (gr) 1/2" 0 3/8" 91.3 #4 505.6 #40 627
#100 119.4 #200 5.6 Pan(-200) 7.3
Core # 1 Center Thickness, in .5 Location SH 155 South bound 500ft north Modulus 215 ksi Asphalt Content 7.92 % Notes: Specimen broke apart while extracting, only 0.5 in thick slurry seal remained intact.
Gradation:
Size (g) 1/2" 2.6 3/8" 135.8 #4 563.5 #40 438.6
#100 158.2 #200 36.2 Pan(-200) 32.1
Intersection District Extraction Date SH 49 & SH 155 Atlanta April 20, 2009
135
Intersection District Extraction Date SH 49 & SH 155 Atlanta April 20, 2009
Core # 1 OWP Thickness, in 2.5 Location SH 155 South bound 500ft north Modulus 256 ksi Asphalt Content 6.99 % Notes:
• Pieces of the specimen were lost during extraction • Low to severe fatigue cracking , rutting, loss of
aggregate, bleeding, pushing, and block cracking • FWD data collected at this location
Gradation:
Size (g) 1/2" 11.5 3/8" 97.8 #4 578.9 #40 545.5
#100 138 #200 5.9 Pan(-200) 6.8
Core # 2 IWP Thickness, in 2.2 Location SH 155 South bound 100ft north Modulus 556 ksi Asphalt Content 7.6 % Notes:
• Low to severe fatigue cracking , rutting, loss of aggregate, bleeding, pushing, and block cracking
• FWD data collected at this location
Gradation
Size (gr) 1/2" 53.9 3/8" 147.4 #4 311 #40 421.8
#100 249.5 #200 111.5 Pan(-200) 46.9
136
Intersection District Extraction Date SH 49 & SH 155 Atlanta April 20, 2009
Core # 2 Center Thickness, in 2.5 Location SH 155 South bound 100ft north Modulus 547 ksi Asphalt Content 8.46 % Notes: Cement detected on the base with Phenolphthalein
Gradation
Size (g) 1/2" 38.6 3/8" 129 #4 373.5 #40 415.3
#100 179.6 #200 109.9 Pan(-200) 73.9
Core # 2 OWP Thickness, in 2.4 Location SH 155 South bound 100ft north Modulus 581 ksi Asphalt Content 7.78 % Notes:
Gradation
Size (g) 1/2" 34.8 3/8" 133.8 #4 359.8 #40 425.7
#100 247.2 #200 108.8 Pan(-200) 17.8
137
Intersection District Extraction Date SH 49 & SH 155 Atlanta April 20, 2009
Core # 3 IWP Thickness, in 4.2 Location SH 49 Eastbound 500ft West Modulus 671 ksi Asphalt Content 4.83 % Notes:
• Cement detected on the base with Phenolphthalein • 42 yards milled by maintenance, severe block cracking
and rutting • T cracking all the way • 10 in treated base
Gradation
Size (gr) 1/2" 57.5 3/8" 141 #4 448 #40 679.8
#100 85.5 #200 7.4 Pan(-200) 4.2
Core # 3 Center Thickness, in 4.2 Location SH 49 Eastbound 500ft West Modulus 562 ksi Asphalt Content 4.93 % Notes:
• Cement detected on the base with Phenolphthalein • 42 yards milled by maintenance, severe block cracking
and rutting • T cracking all the way • 10 in treated base
Gradation
Size (g) 1/2" 35.8 3/8" 152.7 #4 436.2 #40 594.1
#100 141 #200 26 Pan(-200) 31.8
138
Intersection District Extraction Date SH 49 & SH 155 Atlanta April 20, 2009
Core # 3 OWP Thickness, in 4 Location SH 49 Eastbound 500ft West Modulus 590 ksi Asphalt Content 5.4 % Notes: Cement detected on the base with Phenolphthalein
Gradation
Size (g) 1/2" 28.8 3/8" 122.5 #4 437.8 #40 695.6
#100 100.8 #200 9.8 Pan(-200) 12.8
Core # 4 IWP Thickness, in 3.2 Location SH 49 Eastbound 75ft West Modulus 398 ksi Asphalt Content 7.17 % Notes:
Gradation
Size (gr) 1/2" 119.6 3/8" 164.5 #4 310.3 #40 403.9
#100 236.6 #200 128.4 Pan(-200) 27.7
139
Intersection District Extraction Date SH 49 & SH 155 Atlanta April 20, 2009
Core # 4 Center Thickness, in 3.1 Location SH 49 Eastbound 75ft West Modulus 600 ksi Asphalt Content 6.89 % Notes:
Gradation
Size (g) 1/2" 95.4 3/8" 195.8 #4 326.1 #40 377.6
#100 203.7 #200 109.8 Pan(-200) 75
Core # 4 OWP Thickness, in 3.1 Location SH 49 Eastbound 75ft West Modulus 571 ksi Asphalt Content 6.58 % Notes:
Gradation
Size (g) 1/2" 89.6 3/8" 181.6 #4 327.9 #40 394.8
#100 265.5 #200 100.3 Pan(-200) 12.8
140
APPENDIX F: CHECK LISTS FOR FUTURE SITE VISITS
141
Table F.1a: A Checklist of Information that Should be Collected at Intersections (Part1).
Pavement Design of the Intersection Asphalt Layer Thickness Modulus Type of Mix Mix Design Base and/or Subbase Thickness Modulus Stabilized Subgrade Modulus Stabilized Traffic Information from Transportation Planning and Programming Division Traffic predictions for year of construction for each road Traffic predictions for end of analysis period for each road Truck factor for each road Lane distribution Factor for Each Road Truck percentage for each road Geometry of Intersection Number of lanes Direction of each lane Type of signalization Number of Turning lanes
Table F.1b: A Checklist of Information that Should be Collected at Intersections (Part2).
Visual Survey Identify every distress and severity Record total extension (area or length)of every distress Photos of every distress (include a ruler in the close-up images) Surface and subsurface drainage conditions Rut profile depth measurements (use 6 ft straight edge) Rut widths Identify possible locations for testing (FWD, GPR, Coring, Trenching, and DCP) Field Testing Falling Weight Deflectometer (FWD) Test a minimum of 30 points (The most points the better) Decrease the distance between points as approaching the intersection Clearly specify locations
142
Make as many comments on the conditions of the locations as possible Dynamic Cone Penetrometer (DCP) Perform at least one test per core hole Clearly specify locations Repeat test in case tip runs into a rock Ground Penetrating Radar Clearly specify locations Trenching The size of each trench is 3 ft. X 6 ft. Smoothen one of the walls (perpendicular to traffic) Photos (Use chalk or string lines between layers to differentiate) Cores Label Thickness Photo Clearly specify locations Base and Subgrade Sampling Enough material for laboratory testing
Table F.1c: A Checklist of Information that Should be Collected at Intersections (Part3).
Laboratory Testing Asphalt Cores Trim rough surface or base Measure height Weight V-meter Gradation Bulk Specific Gravity (Gmb) Extraction of binder Viscosity of binder Hamburg Wheel Tracking Device on cores IDT strength of cores Complex Modulus and Permanent Deformation on lab specimens prepared at field air
voids NCAT Ignition Base and Subgrade Materials Gradation and Atterberg Limits Moisture Density Curve Texas Triaxial Tests Resilient Modulus/Permanent Deformation Tests at Optimum Moisture Content Resilient Modulus/Permanent Deformation Tests at In-place Moisture Content Moisture Susceptibility
143
In addition several considerations for the data collection process are discussed below.
CURRENT PAVEMENT DESIGN
The first step in every site investigation should be the collection of all the existing data
prior to any visit or analysis. The general pavement information can be obtained from the last
pavement design blueprints. From the cross sectional design of the structure is important to
gather each layer characteristics, for instance thicknesses, type of asphalt mix, type of base, find
if base and/or subgrade are stabilized and which stabilization agents (additives) were used for the
construction. The geometry of the intersection is also essential for the analysis, the number of
lanes in each road and direction as well as the type of signalization needs to be documented.
TRAFFIC INFORMATION
The traffic projections should be requested to the Transportation Planning and
Programming Division. The data obtained should be enough not only to quantify the number of
vehicles (ADT) but the magnitude (ESAL) of traffic loading, which will determine the stresses
induced to the pavement and will allow to classify the road. The AADT for the year of
construction, projected AADT for the end of analysis period, truck factor, lane distribution factor
and truck percentages are needed to calculate the ESALs. If the projected ESALs fro the length
of the analysis period are provided by the TPP the previous information is not needed.
VISUAL SURVEY
Visual surveys serve as a qualitative indicator of the overall pavement condition, for both
functional and structural properties. Specialized equipments and procedures are then used to
quantify both functional and structural aspects of the pavement structure. That is the reason why
the identification of distressed areas to select locations for further inspection is a useful aspect of
condition surveys. The type, extent (area or length), and severity of every distress should be
recorded properly and supported with a photograph, and the predominant distress should be
identified. Rut depths and widths should also be recorded to provide better clues in the
identification of the problematic layer of the structure.
144
NON DESTRUCTIVE TESTING
The most common NDT tools used by TXDOT are FWD, GPR, and DCP. Data collected
from NDT in the filed is generally objective, but subjectivity often appears in the analysis and
interpretation. The most information possible should be collected in the field for the analyst to
carry out a better evaluation and it is of great importance to encourage the operator to write as
many comments as possible on the conditions of the pavement and progress of the test. In the
case of GPR and FWD is extremely important to locate the starting and finishing points of the
analysis, while for the DCP the locations at which the tests were performed. Being the
intersections the main focus of the evaluation is important to increment the number of FWD
collection points as approaching the intersection by reducing the distance between points to 25 ft.
Data collected from NDT is a very useful evaluation tool for the structural support of pavement,
and can be used to evaluate the need for further destructive testing.
DESTRUCTIVE TESTING
Trenching and coring are used to determine the source of the problematic layer when
FWD, GPR, or DCP can not differentiate from which layer the deformation comes from.
Destructive testing provides more detailed data about the mechanical, physical, and chemical
properties of the pavement, information not possible to obtain through NDT. TXDOT has
specific procedures on the Pavement Design Guide for trenching and coring and they should be
followed thoroughly. It is important to take photos of both the trench and cores for
documentation and solve any future doubts. Location of each core hole has to be precisely
recorded and every core has to be labeled and measured at the time of extraction.
145
LABORATORY TESTING
From the cores, base and subgrade materials brought to the laboratory is necessary to
perform the following procedures following TXDOT specifications. A sample summary of the
cores created by CTIS personnel is in Appendix E. The following tests on the asphalt cores are
considered necessary for the analysis.
• Core dimensions
• V-meter
• Gradation
• Bulk Specific Gravity (Gmb)
• Extraction of binder
• Viscosity of binder
• Hamburg Wheel Tracking Device on cores
• IDT strength of cores
• NCAT Ignition
• Complex Modulus and Permanent Deformation on lab specimens at field air voids
For base and subgrade materials the following procedures provide the information necessary for
analysis.
• Gradation and Atterberg Limits
• Moisture Density Curve
• Texas Triaxial Tests
• Resilient Modulus/Permanent Deformation Tests at Optimum Moisture Content
• Resilient Modulus/Permanent Deformation Tests at In-place Moisture Content
• Moisture Susceptibility
146
VITA
Carlos J. Solis was born on August 9, 1983 in Camargo, Mexico. The third son of Carlos
Solis and Victoria Eugenia Lopez, he graduated from Tecnologico de Monterrey High School,
Chihuahua, Mexico in the spring of 2001 and entered the University of Texas at el Paso (UTEP)
in the fall of the same year. He received his bachelor’s degree in Civil Engineering in 2007. In
the spring of 2008 he entered the Civil Engineering graduate program at UTEP.
Permanent address: Calzada Revolucion 451
Cuauhtemoc, Chihuahua, Mexico
This thesis/dissertation was typed by Carlos Solis